Belle Vernon is a borough in Fayette County, Pennsylvania, United States. It is situated along the Monongahela River, abutting two other counties, Westmoreland to the north and Washington across the river. As of the 2020 census, Belle Vernon had a population of 1,025."Bellevernon", as it was originally spelled, was laid out in 1813 by Noah Speers in northwestern Fayette County.