Plymouth CountyHistory of Western Iowa, its settlement and growth. A comprehensive compilation of progressive events concerning the counties, cities, towns, and villages--biographical sketches of the pioneers and business men, with an authentic history of the state of Iowa. Sioux City: Western Publishing Company, 1882. - all bios online*
History of Counties of Woodbury and Plymouth, Iowa [by Will L. Clark, et al.]. Chicago: A. Warner & Co., 1890-91. - see Woodbury Co.
History of Plymouth County, Iowa...ed. by William S. Freeman. 2 vols. Indianapolis, Ind.: B. F. Bowen, 1917. - index, 74 bios online
Other Plymouth County Biographies - 2 bios online