Mahaska County Iowa (Historic Districts) has 7 places on the National Register of Historic Places including 3 places of Statewide significance. Significant places include Lake Keomah State Park, Bathhouse--Lodge Area (Area A), Lake Keomah State Park, Erosion Control Area (Area B) and Penn College Historic District, Edmundson Park Historic District and Lake Keomah State Park, Bathhouse--Lodge Area (Area A).
Some of the country's most noteable architects helped create the Mahaska County places including Ames Central Design Office, Simmons, A.T., and Proudfoot, Bird and Rawson, Douwe Sjaardema, Frank E. Wetherell, Ray F. Wyrick, Iowa Concrete Crib and Silo Co. and Works Progress Administration. Prominent architectural styles found in Mahaska Country are Colonial Revival, Early Commercial and Italianate.