I hear the Snohomish County Jail "John" units on SCSO North (1712) for the most part, on which they will (usually) report to dispatch a prisoner transport.
Ex: "3-John-56 is in service, transporting one inmate from county jail to providence. Beginning mileage is xx." or vice versa. After transport (when arriving back at the jail), they will typically announce that they are out of service.
So I do not believe they use SERS for day-to-day operations over in the jail. From a quick frequency search, I found a trunked 800MHz license located right on top of the jail, so there may be a chance they have their own trunked 800MHz system for jail communication. I unfortunately am not close enough to the jail to verify.
FCC Callsign WPWA883 (Snohomish County 911)
www.radioreference.com