[2] The county was founded on January 15, 1851, and named in honor of John Hancock, a leader of the Continental Congress during the American Revolution.

[4] Hancock county was established as a result of an election on June 28, 1858.

Soon after a courthouse was built in Garner, Iowa that continues to be the county seat.

The racial makeup of the county was 97.70% White, 0.09% Black or African American, 0.10% Native American, 0.31% Asian, 0.02% Pacific Islander, 1.38% from other races, and 0.40% from two or more races.

Of the 4,795 households 32.60% had children under the age of 18 living with them, 60.90% were married couples living together, 6.00% had a female householder with no husband present, and 29.60% were non-families.

[16] Hancock County is divided into sixteen townships: The population ranking of the following table is based on the 2020 census of Hancock County.