Seymour is a city in Jackson County, Indiana, United States. Its population was 17,503 at the 2010 census.
The city is noted for its location at the intersection of two major north/south and east/west railroads, which cross each other in the downtown area. The north/south line was built in the 1840s and connected Indianapolis to the Ohio River at Jeffersonville. In 1852, Capt. Meedy Shields persuaded John Seymour into building the east/west railroad through his land, and in return named the city in Seymour's honor.
The companies Aisin USA and Rose Acre Farms are headquartered in Seymour, and Cummins operates a plant in the area. The city is also home to the second largest high school gymnasium in the United States.