Osseo is a city located in Trempealeau County, Wisconsin, at the confluence of the North and South Forks of the Buffalo River. According to the United States Census Bureau, the city has a total area of 2.1 square miles (5.4 sq. km) of which, 2.1 square miles (5.3 sq.km) of it is land and 0.04 square miles (0.1 sq. km) of it is water. The total area is 0.96% water.