Coatesville (kōtsˈvĭl) [key], city (1990 pop. 11,038), Chester co., SE Pa., on Brandywine Creek, in a farm area; settled c.1717, inc. as a city 1916. It has been a steel center since 1810. Joseph Hergesheimer wrote about this region in The Three Black Pennys. The National Iron and Steel Heritage Museum and the Lukens National Historic District are in Coatesville. The Revolutionary battle of Brandywine (Sept. 11, 1777) was fought to the south of the city; the area is now a state park.