Clay County Population 2018
Clay County's estimated population is 16,170 with a growth rate of -0.95% in the past year according to the most recent United States census data. Clay County is the 46th largest county in Iowa.
| Year | Population | Growth | Growth Rate |
| 2017 | 16,170 | -155 | -0.95% |
| 2016 | 16,325 | -183 | -1.11% |
| 2015 | 16,508 | 17 | 0.10% |
| 2014 | 16,491 | 49 | 0.30% |
| 2013 | 16,442 | -98 | -0.59% |
| 2012 | 16,540 | -55 | -0.33% |
| 2011 | 16,595 | -38 | -0.23% |
| 2010 | 16,633 | -952 | -5.41% |
| 1990 | 17,585 | -1,991 | -10.17% |
| 1980 | 19,576 | 1,112 | 6.02% |
| 1970 | 18,464 | -40 | -0.22% |
| 1960 | 18,504 | 401 | 2.22% |
| 1950 | 18,103 | 341 | 1.92% |
| 1940 | 17,762 | 1,655 | 10.28% |
| 1930 | 16,107 | 447 | 2.85% |
| 1920 | 15,660 | 2,894 | 22.67% |
| 1910 | 12,766 | -635 | -4.74% |
| 1900 | 13,401 | 4,092 | 43.96% |
| 1890 | 9,309 | 5,061 | 119.14% |
| 1880 | 4,248 | 2,725 | 178.92% |
| 1870 | 1,523 | 1,471 | 2828.85% |
| 1860 | 52 | 0.00% |