Majority blue areas will see more Democrat police, majority red (rural) will see more Republican sheriffs.
This is born out by the data I was able to find, but I can't vouch for the veracity: http://verdantlabs.com/politics_of_professions/
Sheriffs and State Troopers are very majority Republican, police are barely majority Democrat.
I suspect that if we had individual data per region, the affiliation would track with the local politics, maybe with +2 R across the board, or something like that.