North Union Township is in the center of Fayette County. It is bordered to the southwest by the city of Uniontown, the county seat. U.S. Route 119 crosses the northern part of the township, leading northeast to Connellsville and southwest to Morgantown, West Virginia. U.S. Route 40, the National Road, forms the southwest border of the township, except where the highway passes through Uniontown; US 40 leads southeast to Cumberland, Maryland, and northwest to Washington, Pennsylvania. The Mon–Fayette Expressway interchanges with US 119 in the Oliver part of the township, just north of Uniontown; the expressway leads northwest to Centerville and southwest to Morgantown.