Riley County Population 2018
Riley County's estimated population is 74,172 with a growth rate of -0.50% in the past year according to the most recent United States census data. Riley County is the 7th largest county in Kansas.
| Year | Population | Growth | Growth Rate |
| 2017 | 74,172 | -376 | -0.50% |
| 2016 | 74,548 | -2,111 | -2.75% |
| 2015 | 76,659 | 364 | 0.48% |
| 2014 | 76,295 | -512 | -0.67% |
| 2013 | 76,807 | -601 | -0.78% |
| 2012 | 77,408 | 4,058 | 5.53% |
| 2011 | 73,350 | 1,786 | 2.50% |
| 2010 | 71,564 | 4,425 | 6.59% |
| 1990 | 67,139 | 3,634 | 5.72% |
| 1980 | 63,505 | 6,717 | 11.83% |
| 1970 | 56,788 | 14,874 | 35.49% |
| 1960 | 41,914 | 8,509 | 25.47% |
| 1950 | 33,405 | 12,788 | 62.03% |
| 1940 | 20,617 | 735 | 3.70% |
| 1930 | 19,882 | -768 | -3.72% |
| 1920 | 20,650 | 4,867 | 30.84% |
| 1910 | 15,783 | 1,955 | 14.14% |
| 1900 | 13,828 | 645 | 4.89% |
| 1890 | 13,183 | 2,753 | 26.40% |
| 1880 | 10,430 | 5,325 | 104.31% |
| 1870 | 5,105 | 3,881 | 317.08% |
| 1860 | 1,224 | 0.00% |