National Register of Historical Places - Plymouth County - Provides a listing of properties, districts, and landmarks in the county. Includes architectural style and period of significance. - http://www.historicdistricts.com/IA/Plymouth/state.html
The Political Graveyard: Plymouth County, Iowa - Database provides political history, cemetery locations, and brief biographies of politicians who were born or lived in the county. - http://politicalgraveyard.com/geo/IA/PM.html#BORN