Killduff is an unincorporated community in southeastern Jasper County, Iowa, United States. It lies along local roads southeast of the city of Newton, the county seat of Jasper County. Its elevation is 922 feet (281 m). Although Killduff is unincorporated, it has a post office with the ZIP code of 50137, which opened on 2 July 1883.
Killduff was once located on the Iowa Central Railway. In 1912, Killduff contained a post office, two stores, a lumber yard, and a blacksmith shop.