Loudoun County Population 2018
Loudoun County's estimated population is 398,080 with a growth rate of 3.06% in the past year according to the most recent United States census data. Loudoun County is the 4th largest county in Virginia.
| Year | Population | Growth | Growth Rate |
| 2017 | 398,080 | 11,801 | 3.06% |
| 2016 | 386,279 | 11,582 | 3.09% |
| 2015 | 374,697 | 11,823 | 3.26% |
| 2014 | 362,874 | 12,016 | 3.42% |
| 2013 | 350,858 | 12,583 | 3.72% |
| 2012 | 338,275 | 11,379 | 3.48% |
| 2011 | 326,896 | 11,296 | 3.58% |
| 2010 | 315,600 | 229,471 | 266.43% |
| 1990 | 86,129 | 28,702 | 49.98% |
| 1980 | 57,427 | 20,277 | 54.58% |
| 1970 | 37,150 | 12,601 | 51.33% |
| 1960 | 24,549 | 3,402 | 16.09% |
| 1950 | 21,147 | 856 | 4.22% |
| 1940 | 20,291 | 439 | 2.21% |
| 1930 | 19,852 | -725 | -3.52% |
| 1920 | 20,577 | -590 | -2.79% |
| 1910 | 21,167 | -781 | -3.56% |
| 1900 | 21,948 | -1,326 | -5.70% |
| 1890 | 23,274 | -360 | -1.52% |
| 1880 | 23,634 | 2,705 | 12.92% |
| 1870 | 20,929 | -845 | -3.88% |
| 1860 | 21,774 | -305 | -1.38% |
| 1850 | 22,079 | 1,648 | 8.07% |
| 1840 | 20,431 | -1,508 | -6.87% |
| 1830 | 21,939 | -763 | -3.36% |
| 1820 | 22,702 | 1,364 | 6.39% |
| 1810 | 21,338 | 815 | 3.97% |
| 1800 | 20,523 | 1,561 | 8.23% |
| 1790 | 18,962 | 0.00% |