Millwood, by the plank road leading to Memphis, and Glencoe, often flooded in the Big Creek area, merged to form Millington around 1875. To stay near the railroad, Glencoe accepted George Millington's land donation on the condition that the town be named for him. It was incorporated in 1903 with W.E. Polk as the first mayor, and its school was the first accredited in Shelby County. National searches selected the town as the site of a World War I aviation training school at Park Field, the world's largest inland Naval Base, and the first USA baseball training site in 1985. The town was declared the state's Flag City in 1986. During World War I, Park Field became a Signal Corps aviation school and one of the first airfields in West Tennessee. Gen. Jas. H. Doolittle often ferried aeroplanes in for Curtiss Aircraft. After World War I, Park Field helped pioneer mail routes over Tennessee and surrounding states. The field was located on the southside parade ground area aboard the Naval Air Station.