Onsted is a village in Lenawee County in the Irish Hills area of the U.S. state of Michigan. The population was 813 at the 2000 census. The fire service in Onsted is provided by the Cambridge Township Fire Department.
According to the United States Census Bureau, the village has a total area of 1.0 square miles (2.5 km²), all land.
As of the census of 2000, there were 813 people, 321 households, and 227 families residing in the village. The population density was 849.7 per square mile (327.0/km²). There were 343 housing units at an average density of 358.5 per square mile (138.0/km²). The racial makeup of the village was 96.92% White, 0.12% African American, 0.62% Native American, 0.12% Asian, 0.25% from other races, and 1.97% from two or more races. Hispanic or Latino of any race were 1.97% of the population.