The city of Jacksonville is in Duval County. A long time ago we incorporated the entire county as the city, to save on duplication of effort. Jacksonville City Limits and Duval County Limits are in exactly the same place. There are other, much smaller townships inside Duval County, which are technically inside Jacksonville City Limits because of that (like Jacksonville Beach, which has its own mayor). The police are the Jacksonville Sheriffs Office. They have JSO on their collars and uniforms. Duval County isn't mentioned at all. So, while it is likely extremely rare, it does happen in real life, at least once.