Mercer is a borough in Mercer County, Pennsylvania, United States, and its county seat. The population was 1,982 at the 2020 census. It is part of the Hermitage micropolitan area.

State Correctional Institution – Mercer is a minimum-security correctional facility near Mercer in the northwestern part of the commonwealth of Pennsylvania. In December of 2025 Mercer held 1,379 inma