https://www.fcc.gov/general/9-1-1-master-psap-registry
https://www.nena.org/?page=911Statistics
https://www.fcc.gov/consumers/guides/911-wireless-services
As of August 2017, the United States has 5,806 primary and secondary PSAPs and 3,135 counties, which include parishes, independent cities, boroughs, and Census areas.
https://www.consumerreports.org/cro/news/2009/05/update-about-911-and-disconnected-landlines/index.htm
http://blog.obihai.com/2014/08/easy-emergency-911-calling-service-with.html
