Onaga is a city in Pottawatomie County, Kansas, United States. As of the 2010 census, the city population was 702. It is part of the Manhattan, Kansas Metropolitan Statistical Area.
Onaga is located at 39°29′22″N 96°10′8″W / 39.48944°N 96.16889°W / 39.48944; -96.16889 (39.489415, -96.168993). According to the United States Census Bureau, the city has an area of 0.6 square miles (1.6 km²), all land.