Dyer (/ˈdaɪər/ DY-ər) is a town in St. John Township, Lake County, Indiana, United States.

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.

Dyer is built on mostly flat land with an exception being the steep sand ridge south of US Highway 30.

Aaron Norton Hart, a settler from Philadelphia, Pennsylvania, played a key role in developing Dyer's infrastructure in the 1860s and 1870s.

Hart supervised construction of roads and the implementation of a drainage ditch system, allowing agricultural and commercial use of the marshy land.

[12] Dyer's primary arterial road is U.S. Route 30/Lincoln Highway, which runs east–west through the town.

A 1.3-mile (2.1 km) stretch of this route traversing Dyer and Schererville was considered one of the most prominent Seedling Mile projects on the Lincoln Highway when it was constructed in the early 1920s, and came to be known as the highway's "Ideal Section."

Mid-America Reformed Seminary is a theological institution located in Dyer.