Iowa's population through the years:
1840-43,112 (including that part of Minnesota lying west of the Mississippi River, which at that time was part of Iowa Territory)
1850-192,214
1860-674,913
1870-1,194,020
1880-1,624,615
1890-1,912,297
1900-2,231,853
1910-2,224,771
1920-2,404,021
1930-2,470,939
1940-2,538,268
1950-2,621,073
1960-2,757,537
Figures from "High Points of Iowa History," by Eugene N. Hastie, 1966