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

The land upriver from Brownsville along the eastern attach of Greene County was acquired by the Youngstown Sheet and Tube Co. (YS&T) which planned, zoned, populated, and built the community, complete later than a movie theater, tennis courts, amusement hall (in the fashion of the get older in blue-collar company towns, part pool hall, part beer garden), and swimming pool near the borough of Carmichaels. At one time, Youngstown Sheet and Tube was the largest steel company in the nation. Establishing the town without difficulty after the United Mine Workers flexed their muscles in the strikes of the 1890s–1900s and after its riot troubles in Youngstown in 1916, it is moreover likely the company had a hand in establishing the local learned and one or more churches and likely issued invitations and recruited the medical practitioners committed the various health clinics.

The mine, established external the town, was one of many large mines atop the Pittsburgh Coal Seam upon the west bank of the Monongahela River. It was operated as a subsidiary under the Buckeye Coal Company and grew and benefited as visceral directly upon the railroad route admin upriver (south) to West Virginia and was dexterous to load both river coal barges and freight trains once its output. It is thought by some to have been the largest coal mine in the United States in 1919, and was rated at innate the second most productive in Greene County in the 1940s war years. The mine operated approximately 70 years, shutting all along production in 1986, and was sealed (safed) 2–3 years later.

Nemacolin is located in the southeast corner of Cumberland Township at 39°52′40″N 79°55′33″W / 39.87778°N 79.92583°W / 39.87778; -79.92583 (39.877676, −79.925858), on the west bank of the Monongahela River, which forms the eastern border of Greene County.