Located at the intersection of Atwood Avenue and Cherry Hill Road, the current Johnston Police Department was completed in 1978. Chief Richard S. Tamburini leads the 72-member department, whose history dates back to the first Town Meeting in 1759, when Johnston appointed Abraham Belknap to the post of Town Sergeant. The Department's history mirrors that of Johnston as a whole, as it has grown with the town's population over the years.

The current structure of the Police Department incudes the Investigative, Uniformed, Operations and Training, Traffic/Special Services, and Nightwatch Divisions. Among the community efforts conducted by the department are in-school Community Resource Officers at Johnston High School and Ferri Middle School; the Citizens Police Academy; self-defense classes; and the weekly Walk with Seniors.