[2] This county is named for Stephen Decatur Jr., a hero in the War of 1812.

[13] At the 2000 census,[14] there were 8,689 people, 3,337 households and 2,149 families residing in the county.

There were 3,833 housing units at an average density of 7 per square mile (2.7/km2).

30.30% of all households were made up of individuals, and 15.50% had someone living alone who was 65 years of age or older.

Decatur County is considered to be the poorest in Iowa, reporting that almost 20% of its residents live in poverty.

[15] Supervisors Steve Fulkerson Doug Tharp Ward Graham Treasurer Janet Pierson Attorney Alan Wilson Auditor Charlene Hoover Recorder Erica Cook Sheriff Chris Lane Assessor Justin Cornett Engineer Justin Savage Clerk of Court Traci Tharp Public Health Administrator Shelley Bickel Veterans Affairs Administrator Samantha Schaff Conservation Director Kayla Clausen Mental Health Director Kathy Lerma Decatur County is divided into these townships: The population ranking of the following table is based on the 2020 census of Decatur County.