Originally Posted by
Stat_Insanity
Corruption has a lot to do with your governors too, I believe. Check the people ruling your cities and see if they have traits like Deep Pockets, Fraudulent, Embezzler, Dubious, Underhanded, and Corrupt. If you're okay with using the console, those can be fixed with the commands:
remove_trait "Governor's Name" Embezzler 3
and
remove_trait "Governor's Name" Corrupt 3
And afterwards moving that governor out of and back into the city to refresh the display. That should help with at least some of it. Your governors will obtain these traits naturally over time, so check pretty often. The only way I know of to stop or slow them getting them is to build up religious buildings in their settlements.