There is a police force in Monitor City. The city could never really attract serious police because there was never much crime, and the whole place had the stigma of an outlaw town anyway. The best candidates they could find to fill the roles were security guards who were having a hard time making it on to real police forces, and who would gladly take a major promotion, despite the location.
The management of the police department was left up to the cops, because most of the MC populace agreed that they had no idea how cops actually did their jobs, and to presume to organize or control them would be foolish. Unfortunately for the populace, the police had no idea how real police operated either, so they made up rules where it seemed important, and just played it loose in general. This is why almost all members of the police department in MC have the title "Detective", and there are no beat cops.
If and when a crime is comitted in MC, the police will dispatch a few detectives to investigate. They will collect evidence and, in the event that it requires some sort of serious analysis, ship it off to the nearest serious crime lab, a private independent satellite office of the FBI in Buffalo, New York. Results typically take a few weeks to come back, but the results go a long way in convincing juries, who almost always ignore non-scientific evidence.
The police fear the MCCS. They know the real power when they see it, and they do their best to stay out of the way. They sometimes make nervous jokes, asking bloodied perps if they want to press charges against couriers, but they never step over the line and actually question a courier. If a courier were to one day go on a murderous rampage in MC, the police would be hard-pressed to stop them, because they very deliberately look the other way when it comes to courier violence.
At the time of this series, there have been six "Chiefs of Police" that have all retired early (boredom and excessive wealth --- they get to set their own salaries), but the current state of the membership is such that no one has outright claimed the title. The closest they have to a leader is Det. Carlos Juarez, but he is more a moral beacon than a serious organizer. Being a criminal in Monitor City these days could land you in hot water, only because the cops need something to do.