Onslow is a city in Jones County, Iowa, United States.

[4] According to the United States Census Bureau, the city has a total area of 0.23 square miles (0.60 km2), all land.

There were 101 housing units at an average density of 520.5 per square mile (201.0/km2).

There were 109 housing units at an average density of 473.9 per square mile (183.0/km2).

The racial makeup of the city was 95.9% White, 2.5% African American, 0.5% Asian, and 1.0% from two or more races.

39.4% of all households were made up of individuals, and 17% had someone living alone who was 65 years of age or older.

There were 107 housing units at an average density of 463.2 per square mile (178.8/km2).

33.3% of all households were made up of individuals, and 22.9% had someone living alone who was 65 years of age or older.

About 15.4% of families and 19.4% of the population were below the poverty line, including 26.5% of those under the age of eighteen and 21.6% of those 65 or over.