The only aircraft that requires an FO is the EMB120. So every EMB120 flight for us will have an FO for sure.
We also have FOs in our SA227s, BE1900s, and BE99s.
The SA227 and BE1900 FOs are by location. Specifically LAN and CVG have the FOs.
The BE99 FOs are across our system (but not in every 99). They are part of our Accelerated Captain Program that puts them right seat in the 99 until they are at our restricted Captain mins.
Hope that helps!