Seymour is a city in Jackson County, Indiana, United States. Its population was 21,569 at the 2020 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, Captain Meedy Shields persuaded a railroad into routing the east-west railroad through his land.