Farrell is a city in western Mercer County, Pennsylvania, United States, along the Shenango River. The population was 4,258 at the 2020 census. It is part of the Hermitage micropolitan area.

Mercer County is a county in the Commonwealth of Pennsylvania. As of the 2020 census, the population was 110,652. Its county seat is Mercer, and its largest city is Hermitage. The county is part of the Northwest Pennsylvania region of the state.