Dyer is a town in St. John Township, Lake County, Indiana, United States. The population was 16,390 at the 2010 census. It is a southeastern suburb of Chicago.
Dyer borders Munster to the north, unincorporated St. John Township to the south, Schererville to the east, and Lynwood and Sauk Village in Illinois to the west. The Illinois state line comprises Dyer's entire western border. One of Dyer's neighborhoods, Briar Ridge, spans both Dyer and adjacent Schererville. Dyer is roughly 30 miles from downtown Chicago and 12 miles from Chicago's south side.
Dyer is built on mostly flat land with an exception being the steep sand ridge south of US Highway 30.