Different jurisdictions handle it differently. In some, the EMA (Emergency Management Agency) runs 9-1-1, which is responsible for scrambling all emergency responses. In others, it could the Sheriff's Office or the county police. In the smaller rural communities around here (I live in South Georgia), dispatchers aren't necessarily POST-certified.
As a former reporter/editor for a daily newspaper, I'd call and visit law enforcement regularly, and I still routinely work with law enforcement in my current position as a Public Health public information officer (Public Health is also a first responder).
Hope this helps. Good luck with your writing.