Resident Population in Marshall County, IA was 40.01400 Thous. of Persons in January of 2023, according to the United States Federal Reserve. Historically, Resident Population in Marshall County, IA reached a record high of 43.00000 in January of 1977 and a record low of 37.90700 in January of 1992. Trading Economics provides the current actual value, an historical data chart and related indicators for Resident Population in Marshall County, IA - last updated from the United States Federal Reserve on May of 2024.