Ottosen is a city in Humboldt County, Iowa, United States.

According to the United States Census Bureau, the city has a total area of 0.57 square miles (1.48 km2), all land.

There were 19 housing units at an average density of 39.1 per square mile (15.1/km2).

There were 26 housing units at an average density of 45.6 per square mile (17.6/km2).

26.1% of all households were made up of individuals, and 8.6% had someone living alone who was 65 years of age or older.

There were 31 housing units at an average density of 54.4 per square mile (21.0/km2).

16.7% of all households were made up of individuals, and 16.7% had someone living alone who was 65 years of age or older.

There were no families and 3.8% of the population living below the poverty line, including no under eighteens and 33.3% of those over 64.