Postal service in the Humboldt County community of Ottosen dates to November 1895, when a post office was first opened within a local siding business near the railroad tracks. The Ottosen office became the first in Humboldt County to have rural routes attached to it, with the first created in 1902. A second was created in 1903, then consolidated in 1932 as delivery methods grew more efficient. Further consolidation has taken place since, with the route now split among several area post offices.

The Ottosen Post Office moved to its present location in February 1957. As of April 2011, the Fort Dodge Messenger is reporting the office may close.