It kind of depends on the department.
A few of the smaller fire departments in Butler County have ALS (Advanced Life Support) units that respond either first or with the dispatch of a medic (ambulance). The ALS unit is usually a paramedic and/or a supervisor, but not always a supervisor. The ALS units are usually paid staff that are already on station so they can respond quickly to provide medical care. Some of the smaller departments rely on part-time/volunteer staff so getting a crew for a medic unit (the ambulance) might require them to get to the station to get the ambulance and then to the call. If the medical care ends up not needing a paramedic and only EMTs, this then also frees up the ALS unit to go back to station. With the smaller departments, staffing is an issue and they might only have a few paramedics, while others are only EMT's.
Generally, in Butler County a medic unit is the ambulance. That doesn't mean it is staffed with paramedics in smaller departments it might only be EMT's.
A few of the larger departments use ASL units like
@scannerboy02 described. They are a paramedic/supervisor that respond and the unit has extra equipment. Most of the larger departments just refer to the ambulance as a medic unit and it is staffed with paramedics.
Other larger departments don't use ASL units at all and the ambulance units are staff with paramedics always.