Osage is a city in Mitchell County, Iowa, United States. The population was 3,619 at the 2010 census. It is the county seat of Mitchell County.
Osage is located at 43°17′5″N 92°48′44″W (43.284618, -92.812129).
According to the United States Census Bureau, the city has a total area of 2.24 square miles (5.80 km2), all land.
As of the census of 2010, there were 3,619 people, 1,614 households, and 954 families living in the city. The population density was 1,615.6 inhabitants per square mile (623.8/km2). There were 1,756 housing units at an average density of 783.9 per square mile (302.7/km2). The racial makeup of the city was 98.1% White, 0.2% African American, 0.1% Native American, 0.3% Asian, 0.6% from other races, and 0.7% from two or more races. Hispanic or Latino of any race were 1.3% of the population.
There were 1,614 households of which 26.0% had children under the age of 18 living with them, 47.1% were married couples living together, 8.9% had a female householder with no husband present, 3.2% had a male householder with no wife present, and 40.9% were non-families. 36.7% of all households were made up of individuals and 21% had someone living alone who was 65 years of age or older. The average household size was 2.16 and the average family size was 2.81.