Sandy Lake is a borough in eastern Mercer County, Pennsylvania, United States. It was established in 1849. The population was 649 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.