ConfigurationManager not found

I had to Install NuGet package System.Configuration.ConfigurationManager in my Visual Studio 2019 C# project.

E.g.,

Install-Package System.Configuration.ConfigurationManager -Version 4.7.0

I had this problem myself and actually included the reference to System.Configuration, and it STILL wouldn't show up.

I had to go to the Build menu, select Clean, and then rebuild.

Posting because in six months when I see this again I'll probably forget what I did...

Make sure you have a reference to the assembly System.Configuration.dll

Project -> Add References -> .NET -> select System.Configuration