Thayer is a city in Neosho County, Kansas, United States. As of the 2010 census, the city population was 497.
Thayer is located at 37°29′14″N 95°28′34″W / 37.48722°N 95.47611°W / 37.48722; -95.47611 (37.487127, -95.476237). According to the United States Census Bureau, the city has a total area of 0.7 square miles (1.9 km²), of which, 0.7 square miles (1.7 km²) of it is land and 0.1 square miles (0.2 km²) of it (9.59%) is water.
As of the census of 2000, there were 500 people, 183 households, and 137 families residing in the city. The population density was 751.5 people per square mile (288.1/km²). There were 203 housing units at an average density of 305.1 per square mile (117.0/km²). The racial makeup of the city was 95.60% White, 1.40% Native American, 1.40% from other races, and 1.60% from two or more races. Hispanic or Latino of any race were 2.20% of the population.