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 irate each further in the downtown area. The north–south line (the Jeffersonville, Madison and Indianapolis Railroad) was built in the 1840s and linked Indianapolis to the Ohio River at Jeffersonville. In 1852, Captain Meedy Shields persuaded Hezekiah Cook Seymour into building the eastwest railroad (the Ohio and Mississippi Railroad) through his land, and in return named the city in Seymour’s honor. The firsts settlers arrived in the spring of 1853.

The companies Aisin USA and Rose Acre Farms are headquartered in Seymour, and Cummins operates a forest in the area. The city is also house to the 2nd largest high school gymnasium in the United States by seating capacity.

Seymour was laid out and plated upon April 27, 1852, near the 1809 Indian Treaty Corner and nearly two miles south of the village of Rockford, Indiana; the terminus of the north-south railroad previously the opening of the purchase of 1828 and the construction of the railbridge higher than the White River. During the latter 1840’s, a north–south railroad connecting the Ohio River at Jeffersonville subsequently Indianapolis was built crossing the Shields’ farm. In 1852, an east–west railroad was bodily surveyed through Jackson County and Meedy Shields persuaded the Ohio and Mississippi Rail Road to control through his property. In dispute for this favor, he utterly to read out the town after the railroad’s civil engineer, Henry C. Seymour, although some sources hint J. Seymour, who was the surveyor.