St. Mary's County, Maryland Population 2019
St. Mary's County, Maryland's estimated population is 112,413 with a growth rate of 0.65% in the past year according to the most recent United States census data. St. Mary's County, Maryland is the 12th largest county in Maryland.
| Year | Population | Growth | Growth Rate |
| 2018 | 112,664 | 251 | 0.22% |
| 2017 | 112,413 | 724 | 0.65% |
| 2016 | 111,689 | 724 | 0.65% |
| 2015 | 110,965 | 1,039 | 0.95% |
| 2014 | 109,926 | 698 | 0.64% |
| 2013 | 109,228 | 423 | 0.39% |
| 2012 | 108,805 | 1,247 | 1.16% |
| 2011 | 107,558 | 1,796 | 1.70% |
| 2010 | 105,762 | 29,788 | 39.21% |
| 1990 | 75,974 | 16,079 | 26.85% |
| 1980 | 59,895 | 12,507 | 26.39% |
| 1970 | 47,388 | 8,473 | 21.77% |
| 1960 | 38,915 | 9,804 | 33.68% |
| 1950 | 29,111 | 14,485 | 99.04% |
| 1940 | 14,626 | -563 | -3.71% |
| 1930 | 15,189 | -923 | -5.73% |
| 1920 | 16,112 | -918 | -5.39% |
| 1910 | 17,030 | -152 | -0.88% |
| 1900 | 17,182 | 1,363 | 8.62% |
| 1890 | 15,819 | -1,115 | -6.58% |
| 1880 | 16,934 | 1,990 | 13.32% |
| 1870 | 14,944 | -269 | -1.77% |
| 1860 | 15,213 | 1,515 | 11.06% |
| 1850 | 13,698 | 474 | 3.58% |
| 1840 | 13,224 | -235 | -1.75% |
| 1830 | 13,459 | 485 | 3.74% |
| 1820 | 12,974 | 180 | 1.41% |
| 1810 | 12,794 | -905 | -6.61% |
| 1800 | 13,699 | -1,845 | -11.87% |
| 1790 | 15,544 | 0.00% |