Where is NuGet.Config file located in Visual Studio project?

I am wondering where is NuGet.Config file located in Visual Studio 2017 project? I tried to create my own NuGet.Config file in the root of the project, but I didn't find any new repositories (NuGet sources). Does some one have any idea?

Here is the file I am trying to achieve for my .Net Core project:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <packageSources>
    <add key="AspNetCore" value="https://dotnet.myget.org/F/aspnetcore-ci-dev/api/v3/index.json" />
    <add key="AspNetCoreTools" value="https://dotnet.myget.org/F/aspnetcore-tools/api/v3/index.json" />
    <add key="NuGet" value="https://api.nuget.org/v3/index.json" />
  </packageSources>
</configuration>

Visual Studio reads NuGet.Config files from the solution root. Try moving it there instead of placing it in the same folder as the project.

You can also place the file at %appdata%\NuGet\NuGet.Config and it will be used everywhere.

https://docs.microsoft.com/en-us/nuget/schema/nuget-config-file

There are multiple nuget packages read in the following order:

1. First the NuGetDefaults.Config file. You will find this in %ProgramFiles(x86)%\NuGet\Config.
2. The computer-level file.
3. The user-level file. You will find this in %APPDATA%\NuGet\nuget.config.
4. Any file named nuget.config beginning from the root of your drive up to the directory where nuget.exe is called.
5. The config file you specify in the -configfile option when calling nuget.exe

You can find more information here.

In addition to the accepted answer, I would like to add one info, that NuGet packages in Visual Studio 2017 are located in the project file itself. I.e., right click on the project -> edit, to find all package reference entries.

If you use proxy, you will have to edit the Nuget.config file.

In Windows 7 and 10, this file is in the path:
C:\Users\YouUser\AppData\Roaming\NuGet.

Include the setting:

<config>
  <add key = "http_proxy" value = "http://Youproxy:8080" />
  <add key = "http_proxy.user" value = "YouProxyUser" />
</config>