Nemacolin is a census-designated place (CDP) in Greene County, Pennsylvania, United States. It was founded as a company town around the workings of a Youngstown Sheet and Tube Company that owned and operated a coal mine in 1917. The name reflects a noted Amerindian ally Chief Nemacolin, who showed the Virginia and Pennsylvania settlers how to cross the successive Allegheny barrier ridges via the Cumberland Narrows and the Nemacolin Trail—which Braddock Expedition widened into a wagon road through the mountains. The population of the CDP was 937 at the 2010 census.

Greene County is a county in the Commonwealth of Pennsylvania. As of the 2020 census, the population was 35,954. Its county seat is Waynesburg. Greene County was created on February 9, 1796, from part of Washington County and named for General Nathanael Greene. The county is part of the Southwest Pennsylvania region of the state.