First, I'm not a computer expert so keep that in mind.I'm really lost here.
However, after doing some searching on the C Drive, I found program files and SImcity 4 deluxe under program files. I then see the regions folder with only the regions that shipped with the game.
I see none of the regions that I created or any regions I have tried to download.
I go into My documents and see Simcity 4 and check the regions folder. All my created regions and regions I have tried to download are here, plus all the mods in the plugin folder. So my guess is that I did put it in my Documents folder, like I originally thought.