| Population development |
| Census | Inhabitants | | ± in % |
| 1840 | 43.112 | | - — |
| 1850 | 192.214 | | 345,8 % |
| 1860 | 674.913 | | 251,1 % |
| 1870 | 1.194.020 | | 76,9 % |
| 1880 | 1.624.615 | | 36,1 % |
| 1890 | 1.912.297 | | 17,7 % |
| 1900 | 2.231.853 | | 16,7 % |
| 1910 | 2.224.771 | | −0,3 % |
| 1920 | 2.404.021 | | 8,1 % |
| 1930 | 2.470.939 | | 2,8 % |
| 1940 | 2.538.268 | | 2,7 % |
| 1950 | 2.621.073 | | 3,3 % |
| 1960 | 2.757.537 | | 5,2 % |
| 1970 | 2.824.376 | | 2,4 % |
| 1980 | 2.913.808 | | 3,2 % |
| 1990 | 2.776.755 | | −4,7 % |
| 2000 | 2.926.324 | | 5,4 % |
| 2010 | 3.046.355 | | 4,1 % |
| Estimate 2018 | 3.156.145 | | 3,6 % |
| Before 1900 1900–1990 2000 |
Iowa has a population of 3,156,145 (2018 estimate), of which 88.7 percent are white, 5.0 percent are Hispanic or Latino, 2.9 percent are black or African American, 1.7 percent are Asian American, and 0.4 percent are descendants of Native Americans.
Most Iowa residents have European ancestors. The ethnic Germans are by far the largest group with about 36 percent (2014). The Amana Colonies on the Iowa River still have a German influence today.
Religions
The largest religious community in Iowa is the Roman Catholic Church, to which about 23 percent of the population belong. The individual Protestant denominations are significantly less strongly represented. However, if the various Protestant groups are added together, Iowa is more Protestant. The religious denominations with the most members in 2000 were the Catholic Church with 558,092, the Evangelical Lutheran Church in America with 268,543, and the United Methodist Church with 248,211 adherents.
Known became the building "Trinity Church" of the village of Manning. Because of the reduced congregation, it was laboriously transported on a flatbed truck to a place 10 km away.
When asked "What is your religion?" in 2001, Iowa residents answered:
Largest cities
See also: List of localities in Iowa