what county is havana,il in?
Sponsored Topics. Havana is a city in Mason County, Illinois, United States. The population was 3,577 at the 2000 census, and 3,260 at a 2009 estimate. It is the county seat of Mason County. Havana is located on the Illinois River at 40Â°17â²49â³N 90Â°3â²36â³W / 40.29694Â°N 90.06Â°W / 40.29694; -90.06 (40.297067, -90.060004).