It can vary from state to state. In CA, unless they have changed in the last eight months or so, from a cell you will get the California Highway Patrol, no matter where you are in the state. It should be the nearest CHP dispatch center, but cell sites do strange things some time. The CHP dispatcher will then transfer you to the appropriate agency, assuming that you aren't calling in a traffic problem.

And by law a 911 call can only be transferred one time, so you'd better hope that you get the correct agency by that time, or which every dispatch you have by then will be the one you are stuck with...