Much of Los Angeles County's role is to administer the criminal justice system. The Superior Court is no longer a county department (although it was for much of the county's history). But the indepedently elected sheriff and district attorney are both county offices. So are the public defender and the alternate public defender. The Countywide Criminal Justice Coordination Committee brings those offices, and non-county offices as well, together.
When police come in the form of large contingents of federal agents who dress and behave like soldiers, they can for all practical purposes occupy cities militarily just as surely as the Marines or the National Guard.
The buildings aren't the problem - it's the probation officers.