Modern high security prisons are engineered to some degree to repel a determined assault. A lot of (if not most) regular county jails are extremely high security compared to regular prisons, but personnel issues are what make the difference between one engineered to repel an assault or not. Most can simply "lock down" and wait for the cavalry to arrive and if the assaulting force does not have the means to breach multiple steel and concrete doors quickly, they are not getting in.