The main part of Osakis is in Douglas County; only a small part of the city extends into Todd County.
There were 661 households out of which 26.2% had children under the age of 18 living with them, 50.2% were married couples living together, 7.4% had a female householder with no husband present, and 38.7% were non-families. 34.8% of all households were made up of individuals and 22.4% had someone living alone who was 65 years of age or older. The average household size was 2.23 and the average family size was 2.84.
In the city the population was spread out with 22.0% under the age of 18, 6.8% from 18 to 24, 21.4% from 25 to 44, 20.2% from 45 to 64, and 29.7% who were 65 years of age or older. The median age was 45 years. For every 100 females there were 90.2 males. For every 100 females age 18 and over, there were 85.0 males.
The median income for a household in the city was $29,833, and the median income for a family was $38,864. Males had a median income of $28,819 versus $20,000 for females. The per capita income for the city was $15,212. About 5.6% of families and 9.1% of the population were below the poverty line, including 8.1% of those under age 18 and 13.7% of those age 65 or over.