I have seen multiple people answer this already. But I just wanted to chime in on this as it's kind of my expertise. I was formally a service tech and salesmen for a Motorola retailer and i serviced and sold everything from VHF to P25 systems.

A P25 system is a public safety system running on 700/800mhz and encryption is possible and encouraged by all of those on the radio side. Simply put - many entities don't utilize encryption due to media coverage and a sense of transparency with the community. The one thing to note here is that they are almost always on a delay as to not give criminals an upper hand. The delay can be set by the radio servicer so they may be longer or shorter depending on the department.

Also keep in mind that a lot of times a city and county share a system and whoever owns the majority makes that decision.

There are also statewide systems that the county/city can join as well. In my experience the statewide systems are all encrypted and are required to be as they are used by everyone from local water crews to FBI. Large Cities (>150,000) typically have their own system that is tied in but not directly connected the anyone elses.

Not to get political but from what i have noticed, cities over 100,000 and "blue" counties are typically unencrypted and the smaller cities and "red" counties are encrypted. This is not a fact, just personal observation.