The thermostats in county lockups are set to a temperature which will keep corrections officers comfortable while they work their shifts and walk their rounds.
Fuck inmates.
The jail I served in was a relatively new building with central air conditioning, and in my experience, was bracingly cold both winter and summer.
I slept on the actual wall mounted metal bunk in my cell, as opposed to the folding cots they would stuff in corners to make a single occupancy cell hold two or more inmates, but that meant the ceiling vent was perpetually aimed right straight at my face during the night, blasting frigid air, cold enough to refrigerate a walk-in beer cooler.
Everybody wears their orange jumper to bed, preferably with a sweatshirt underneath and thick crew socks to boot.
The blankets are typically a rough wool blend, both uncomfortable and aerated, due to being pockmarked with cigarette burns, despite the jail being a non-smoking facility.
I discovered that I could get reasonably comfortable for at least a few minutes a day, if I timed my shower to be just after a meal. That way, the push button nozzle in the stainless steel stall (no temperature control) would emit a pleasantly warm (as opposed to its typically scalding hot) spray, due to the industrial grade dishwasher in the kitchen monopolizing the output of the quick recovery water heater.
It really does take that sort of strategic calculation to be comfortable in jail.
Layering is essential.