Thayer is a village in Sangamon County, Illinois, United States.

It is part of the Springfield, Illinois Metropolitan Statistical Area.

[2] According to the 2010 census, Thayer has a total area of 0.61 square miles (1.58 km2), all land.

There were 288 housing units at an average density of 479.4 per square mile (185.1/km2).

21.4% of all households were made up of individuals, and 10.9% had someone living alone who was 65 years of age or older.