Piatt County Population 2018
Piatt County's estimated population is 16,445 with a growth rate of -0.49% in the past year according to the most recent United States census data. Piatt County is the 66th largest county in Illinois.
| Year | Population | Growth | Growth Rate |
| 2017 | 16,445 | -81 | -0.49% |
| 2016 | 16,526 | 174 | 1.06% |
| 2015 | 16,352 | -59 | -0.36% |
| 2014 | 16,411 | -20 | -0.12% |
| 2013 | 16,431 | -71 | -0.43% |
| 2012 | 16,502 | -177 | -1.06% |
| 2011 | 16,679 | -32 | -0.19% |
| 2010 | 16,711 | 1,163 | 7.48% |
| 1990 | 15,548 | -1,033 | -6.23% |
| 1980 | 16,581 | 1,072 | 6.91% |
| 1970 | 15,509 | 549 | 3.67% |
| 1960 | 14,960 | 990 | 7.09% |
| 1950 | 13,970 | -689 | -4.70% |
| 1940 | 14,659 | -929 | -5.96% |
| 1930 | 15,588 | -126 | -0.80% |
| 1920 | 15,714 | -662 | -4.04% |
| 1910 | 16,376 | -1,330 | -7.51% |
| 1900 | 17,706 | 644 | 3.77% |
| 1890 | 17,062 | 1,479 | 9.49% |
| 1880 | 15,583 | 4,630 | 42.27% |
| 1870 | 10,953 | 4,826 | 78.77% |
| 1860 | 6,127 | 4,521 | 281.51% |
| 1850 | 1,606 | 0.00% |