diff --git a/src/libraries/System.Text.Json/src/System.Text.Json.csproj b/src/libraries/System.Text.Json/src/System.Text.Json.csproj
index 0a80a0e73974c8..b588e933c2acba 100644
--- a/src/libraries/System.Text.Json/src/System.Text.Json.csproj
+++ b/src/libraries/System.Text.Json/src/System.Text.Json.csproj
@@ -21,6 +21,7 @@ The System.Text.Json library is built-in as part of the shared framework in .NET
   </PropertyGroup>
 
   <ItemGroup>
+    <Compile Include="$(CommonPath)Polyfills\ReflectionPolyfills.cs" Link="Common\Polyfills\ReflectionPolyfills.cs" />
     <Compile Include="$(CommonPath)System\HexConverter.cs" Link="Common\System\HexConverter.cs" />
     <Compile Include="$(CommonPath)System\Net\ArrayBuffer.cs" Link="Common\System\Net\ArrayBuffer.cs" />
     <Compile Include="$(CommonPath)System\Text\ValueStringBuilder.cs" Link="Common\ValueStringBuilder.cs" />
diff --git a/src/libraries/System.Text.Json/src/System/ReflectionExtensions.cs b/src/libraries/System.Text.Json/src/System/ReflectionExtensions.cs
index a8acfb552f2f99..9e7d70d5d2e931 100644
--- a/src/libraries/System.Text.Json/src/System/ReflectionExtensions.cs
+++ b/src/libraries/System.Text.Json/src/System/ReflectionExtensions.cs
@@ -45,7 +45,7 @@ public static bool IsInSubtypeRelationshipWith(this Type type, Type other) =>
             type.IsAssignableFromInternal(other) || other.IsAssignableFromInternal(type);
 
         private static bool HasJsonConstructorAttribute(ConstructorInfo constructorInfo)
-            => constructorInfo.GetCustomAttribute<JsonConstructorAttribute>() is not null;
+            => constructorInfo.IsDefined(typeof(JsonConstructorAttribute), inherit: false);
 
         public static bool HasRequiredMemberAttribute(this MemberInfo memberInfo)
         {
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/MemberAccessor.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/MemberAccessor.cs
index 248a560cd58ce6..6695b503e09fd5 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/MemberAccessor.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/MemberAccessor.cs
@@ -49,7 +49,7 @@ static MemberAccessor Initialize()
 
         public abstract Func<object>? CreateParameterlessConstructor(Type type, ConstructorInfo? constructorInfo);
 
-        public abstract Func<object[], T> CreateParameterizedConstructor<T>(ConstructorInfo constructor);
+        public abstract Func<object?[], T> CreateParameterizedConstructor<T>(ConstructorInfo constructor);
 
         public abstract JsonTypeInfo.ParameterizedConstructorDelegate<T, TArg0, TArg1, TArg2, TArg3>? CreateParameterizedConstructor<T, TArg0, TArg1, TArg2, TArg3>(ConstructorInfo constructor);
 
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/ReflectionEmitCachingMemberAccessor.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/ReflectionEmitCachingMemberAccessor.cs
index 099c1fb0f93e54..0d80689e660a69 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/ReflectionEmitCachingMemberAccessor.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/ReflectionEmitCachingMemberAccessor.cs
@@ -53,7 +53,7 @@ public override Func<IEnumerable<TElement>, TCollection> CreateImmutableEnumerab
                 key: (nameof(CreateImmutableEnumerableCreateRangeDelegate), typeof((TCollection, TElement)), null),
                 valueFactory: _ => _sourceAccessor.CreateImmutableEnumerableCreateRangeDelegate<TCollection, TElement>());
 
-        public override Func<object[], T> CreateParameterizedConstructor<T>(ConstructorInfo constructor) =>
+        public override Func<object?[], T> CreateParameterizedConstructor<T>(ConstructorInfo constructor) =>
             _cache.GetOrAdd(
                 key: (nameof(CreateParameterizedConstructor), typeof(T), constructor),
                 valueFactory: key => _sourceAccessor.CreateParameterizedConstructor<T>((ConstructorInfo)key.member!));
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/ReflectionEmitMemberAccessor.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/ReflectionEmitMemberAccessor.cs
index 5a9fde9c017305..836954b24872a3 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/ReflectionEmitMemberAccessor.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/ReflectionEmitMemberAccessor.cs
@@ -68,8 +68,8 @@ public ReflectionEmitMemberAccessor()
             return CreateDelegate<Func<object>>(dynamicMethod);
         }
 
-        public override Func<object[], T> CreateParameterizedConstructor<T>(ConstructorInfo constructor) =>
-            CreateDelegate<Func<object[], T>>(CreateParameterizedConstructor(constructor));
+        public override Func<object?[], T> CreateParameterizedConstructor<T>(ConstructorInfo constructor) =>
+            CreateDelegate<Func<object?[], T>>(CreateParameterizedConstructor(constructor));
 
         private static DynamicMethod CreateParameterizedConstructor(ConstructorInfo constructor)
         {
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/ReflectionMemberAccessor.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/ReflectionMemberAccessor.cs
index b0d9f2503f0840..775cb1323b07c3 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/ReflectionMemberAccessor.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/ReflectionMemberAccessor.cs
@@ -34,10 +34,15 @@ public ReflectionMemberAccessor()
                     : null;
             }
 
+#if NET
+            ConstructorInvoker invoker = ConstructorInvoker.Create(ctorInfo);
+            return invoker.Invoke;
+#else
             return () => ctorInfo.InvokeNoWrapExceptions(null);
+#endif
         }
 
-        public override Func<object[], T> CreateParameterizedConstructor<T>(ConstructorInfo constructor)
+        public override Func<object?[], T> CreateParameterizedConstructor<T>(ConstructorInfo constructor)
         {
             Type type = typeof(T);
 
@@ -46,22 +51,24 @@ public override Func<object[], T> CreateParameterizedConstructor<T>(ConstructorI
 
             int parameterCount = constructor.GetParameters().Length;
 
+#if NET
+            ConstructorInvoker invoker = ConstructorInvoker.Create(constructor);
+            return arguments => (T)invoker.Invoke(arguments.AsSpan(0, parameterCount));
+#else
             return (arguments) =>
             {
                 // The input array was rented from the shared ArrayPool, so its size is likely to be larger than the param count.
                 // The emit equivalent of this method does not (need to) allocate here + transfer the objects.
                 object[] argsToPass = new object[parameterCount];
 
-                for (int i = 0; i < parameterCount; i++)
-                {
-                    argsToPass[i] = arguments[i];
-                }
+                Array.Copy(arguments, 0, argsToPass, 0, parameterCount);
 
                 // Not wrapping in TargetInvocationException also plumbs ArgumentException through for
                 // tuples with more than 7 generic parameters, e.g.
                 // System.ArgumentException : The last element of an eight element tuple must be a Tuple.
                 return (T)constructor.InvokeNoWrapExceptions(argsToPass);
             };
+#endif
         }
 
         public override JsonTypeInfo.ParameterizedConstructorDelegate<T, TArg0, TArg1, TArg2, TArg3>?
@@ -73,36 +80,55 @@ public override JsonTypeInfo.ParameterizedConstructorDelegate<T, TArg0, TArg1, T
             Debug.Assert(constructor.DeclaringType == type && !constructor.IsStatic);
 
             int parameterCount = constructor.GetParameters().Length;
+#if NET
+            ConstructorInvoker invoker = ConstructorInvoker.Create(constructor);
+#endif
 
             Debug.Assert(parameterCount <= JsonConstants.UnboxedParameterCountThreshold);
 
             return (arg0, arg1, arg2, arg3) =>
             {
-                object[] arguments = new object[parameterCount];
+#if NET
+                switch (parameterCount)
+                {
+                    case 0:
+                        return (T)invoker.Invoke();
+                    case 1:
+                        return (T)invoker.Invoke(arg0);
+                    case 2:
+                        return (T)invoker.Invoke(arg0, arg1);
+                    case 3:
+                        return (T)invoker.Invoke(arg0, arg1, arg2);
+                    case 4:
+                        return (T)invoker.Invoke(arg0, arg1, arg2, arg3);
+                    default:
+                        Debug.Fail("We shouldn't be here if there are more than 4 parameters.");
+                        throw new InvalidOperationException();
+                }
+#else
+                object?[] arguments = new object?[parameterCount];
 
-                for (int i = 0; i < parameterCount; i++)
+                switch (parameterCount)
                 {
-                    switch (i)
-                    {
-                        case 0:
-                            arguments[0] = arg0!;
-                            break;
-                        case 1:
-                            arguments[1] = arg1!;
-                            break;
-                        case 2:
-                            arguments[2] = arg2!;
-                            break;
-                        case 3:
-                            arguments[3] = arg3!;
-                            break;
-                        default:
-                            Debug.Fail("We shouldn't be here if there are more than 4 parameters.");
-                            throw new InvalidOperationException();
-                    }
+                    case > 4:
+                        Debug.Fail("We shouldn't be here if there are more than 4 parameters.");
+                        throw new InvalidOperationException();
+                    case 4:
+                        arguments[3] = arg3;
+                        goto case 3;
+                    case 3:
+                        arguments[2] = arg2;
+                        goto case 2;
+                    case 2:
+                        arguments[1] = arg1;
+                        goto case 1;
+                    case 1:
+                        arguments[0] = arg0;
+                        break;
                 }
 
                 return (T)constructor.InvokeNoWrapExceptions(arguments);
+#endif
             };
         }
 
@@ -114,10 +140,12 @@ public override JsonTypeInfo.ParameterizedConstructorDelegate<T, TArg0, TArg1, T
             Debug.Assert(constructor.DeclaringType == type && !constructor.IsStatic);
             Debug.Assert(constructor.GetParameters().Length == 1);
 
-            return value =>
-            {
-                return (T)constructor.InvokeNoWrapExceptions(new object?[] { value });
-            };
+#if NET
+            ConstructorInvoker invoker = ConstructorInvoker.Create(constructor);
+            return value => (T)invoker.Invoke(value);
+#else
+            return value => (T)constructor.InvokeNoWrapExceptions(new object?[] { value });
+#endif
         }
 
         public override Action<TCollection, object?> CreateAddMethodDelegate<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods)] TCollection>()
@@ -127,11 +155,12 @@ public override JsonTypeInfo.ParameterizedConstructorDelegate<T, TArg0, TArg1, T
 
             // We verified this won't be null when we created the converter for the collection type.
             MethodInfo addMethod = (collectionType.GetMethod("Push") ?? collectionType.GetMethod("Enqueue"))!;
-
-            return delegate (TCollection collection, object? element)
-            {
-                addMethod.InvokeNoWrapExceptions(collection, new object[] { element! });
-            };
+#if NET
+            MethodInvoker invoker = MethodInvoker.Create(addMethod);
+            return (collection, element) => invoker.Invoke(collection, element);
+#else
+            return (collection, element) => addMethod.InvokeNoWrapExceptions(collection, new object[] { element });
+#endif
         }
 
         public override Func<IEnumerable<TElement>, TCollection> CreateImmutableEnumerableCreateRangeDelegate<TCollection, TElement>()
@@ -151,31 +180,41 @@ public override Func<IEnumerable<KeyValuePair<TKey, TValue>>, TCollection> Creat
         public override Func<object, TProperty> CreatePropertyGetter<TProperty>(PropertyInfo propertyInfo)
         {
             MethodInfo getMethodInfo = propertyInfo.GetMethod!;
-
-            return delegate (object obj)
-            {
-                return (TProperty)getMethodInfo.InvokeNoWrapExceptions(obj, null)!;
-            };
+#if NET
+            MethodInvoker invoker = MethodInvoker.Create(getMethodInfo);
+            return obj => (TProperty)invoker.Invoke(obj)!;
+#else
+            return obj => (TProperty)getMethodInfo.InvokeNoWrapExceptions(obj, null)!;
+#endif
         }
 
+        private delegate TProperty ValueTypePropertyGetter<TProperty, TDeclaringType>(ref TDeclaringType obj);
+
         public override Func<TDeclaringType, TProperty> CreatePropertyGetter<TDeclaringType, TProperty>(PropertyInfo propertyInfo)
         {
             MethodInfo getMethodInfo = propertyInfo.GetMethod!;
 
-            return delegate (TDeclaringType obj)
+            // If TDeclaringType is a value type, the instance is passed by reference,
+            // so we need to create a wrapper delegate to account for this.
+            if (typeof(TDeclaringType).IsValueType)
             {
-                return (TProperty)getMethodInfo.InvokeNoWrapExceptions(obj, null)!;
-            };
+                ValueTypePropertyGetter<TProperty, TDeclaringType> f = getMethodInfo.CreateDelegate<ValueTypePropertyGetter<TProperty, TDeclaringType>>();
+                return obj => f(ref obj);
+            }
+
+            return getMethodInfo.CreateDelegate<Func<TDeclaringType, TProperty>>();
         }
 
         public override Action<object, TProperty> CreatePropertySetter<TProperty>(PropertyInfo propertyInfo)
         {
             MethodInfo setMethodInfo = propertyInfo.SetMethod!;
 
-            return delegate (object obj, TProperty value)
-            {
-                setMethodInfo.InvokeNoWrapExceptions(obj, new object[] { value! });
-            };
+#if NET
+            MethodInvoker invoker = MethodInvoker.Create(setMethodInfo);
+            return (obj, value) => invoker.Invoke(obj, value);
+#else
+            return (obj, value) => setMethodInfo.InvokeNoWrapExceptions(obj, new object[] { value });
+#endif
         }
 
         public override Func<object, TProperty> CreateFieldGetter<TProperty>(FieldInfo fieldInfo) =>