Jarrettsville is an unincorporated community and census-designated place (CDP) in Harford County, Maryland, United States. The population was 2,888 at the 2020 census.

Harford County is a county located in the U.S. state of Maryland. As of the 2020 census, the population was 260,924. Its county seat is Bel Air. Harford County is included in the Baltimore-Columbia-Towson, MD Metropolitan Statistical Area, which is also included in the Washington-Baltimore-Arlington, DC-MD-VA-WV-PA Combined Statistical Area.