applicationhost.config file path in IIS 7, 7.5, 8, 8.5 and IIS 10?

For the “big” IIS versions since IIS 7, the location is always the same:

 %windir%\System32\inetsrv\config\applicationHost.config

For IIS Express there is one per user, the default location is:

%USERPROFILE%\Documents\IISExpress\config\applicationhost.config

again it’s the same for all versions.

You can run multiple instances of IIS Express per user, you would need to specify the location of the applicationhost.config as the command line parameter /config for iisexpress.exe