I think the DC area must have the highest concentration of police per capita.
In Virginia and Maryland we have, of course, the state police, county police, county sheriff, and city police like everybody else. DC has its own city police.
We also have a lot of federal parkland, particularly the George Washington Parkway, which is also a major commuter route, patrolled by the National Park Police.
CIA headquarters is in McLean, and that area occasionally crawls with oddly nondescript police cars with federal plates marked only as “Police.”
Most people think of the Secret Service as those guys in dark suits with curly wires stuck in their ears and bulges in their jackets, but in DC you see the uniformed Secret Service, driving marked cars.
There is also a mysterious fleet of unmarked black SUVs with DC plates, all starting with “BJ” <write your own joke here> that randomly run around the city in caravans of 2-3 with hidden* emergency lights flashing, demanding passage through traffic for no apparent emergency reason (I suspect they are taking congressmen to the chamber for a vote but they bear DC, not federal, plates).
The DC Housing Authority has a police force.
I’m sure I’m missing some. And, really. Does the Government Printing Office need its own police force?
*By *hidden *I mean they are visible when flashing but otherwise hiding behind grills and tinted glass, no rooftop light bars.