Onaga is a city in Pottawatomie County, Kansas, United States.

[4] Onaga is derived from a Potawatomi personal Indian name (Onago) and was given by Paul E. Havens, President of the Kansas Central Railroad.

According to the United States Census Bureau, the city has a total area of 0.64 square miles (1.66 km2), all land.

[8] This climatic region is typified by large seasonal temperature differences, with warm to hot (and often humid) summers and cold (sometimes severely cold) winters.

[9] Onaga is part of the Manhattan, Kansas Metropolitan Statistical Area.

The 2020 United States census counted 679 people, 267 households, and 156 families in Onaga.

There were 324 housing units at an average density of 493.9 per square mile (190.7/km2).

38.6% of households consisted of individuals and 21.7% had someone living alone who was 65 years of age or older.

37.8% of all households were made up of individuals, and 21.6% had someone living alone who was 65 years of age or older.

40.8% of all households were made up of individuals, and 25.7% had someone living alone who was 65 years of age or older.

The community is served by Onaga USD 322 public school district.