Coatesville is a city in Chester County, Pennsylvania, United States. The population was 13,350 at the 2020 census. Coatesville is approximately 39 miles west of Philadelphia. It developed along the Philadelphia and Lancaster Turnpike beginning in the late 18th century. It spans U.S. Route 30, the "Main Line" highway that runs west of Philadelphia. Coatesville developed in the early 20th century with the growth of the Lukens Steel Company and other industry.