| Native born. | Native White—Foreign Parents. | |||||
| Male | 10,634 | Male | 114 | |||
| Female | 11,213 | Female | 121 | |||
| Foreign born. | Foreign White. | |||||
| Male | 59 | Male | 58 | |||
| Female | 42 | Female | 42 | |||
| Native White—Native Parents. | Total Colored | |||||
| Male | 7,583 | Male | 2,938 | |||
| Female | 8,161 | Female | 2,931 | |||
In 1860, one year before the outbreak of the Civil War, the County held within its boundaries 21,774 souls: 15,021 white, 5,501 slave, and 1,252 free colored. In number of slaves at this period Loudoun ranked thirty-sixth in the list of Virginia counties which then also included the counties now in West Virginia. This number was distributed amongst 670 slave-holders in the following proportions:
| 1 slave | 124 | |||
| 2 slaves | 84 | |||
| 3 slaves | 61 | |||
| 4 slaves | 83 | |||
| 5 slaves | 46 | |||
| 6 slaves | 39 | |||
| 7 slaves | 35 | |||
| 8 slaves | 27 | |||
| 9 slaves | 22 | |||
| 10 and under 15 slaves | 80 | |||
| 15 and under 20 slaves | 36 | |||
| 20 and under 30 slaves | 23 | |||
| 30 and under 40 slaves | 4 | |||
| 40 and under 50 slaves | 4 | |||
| 50 and under 70 slaves | 1 | |||
| 100 and under 200 slaves | 1 |
The following table gives the population of Loudoun County decennially, from and including the first official census of 1790:
| 1900 | 21,948 | |||
| 1890 | 23,274 | |||
| 1880 | 23,634 | |||
| 1870 | 20,929 | |||
| 1860 | 21,774 | |||
| 1850 | 22,079 | |||
| 1840 | 20,431 | |||
| 1830 | 21,939 | |||
| 1820 | 22,702 | |||
| 1810 | 21,338 | |||
| 1800 | 20,523 | |||
| 1790 | 18,952 |
The reports of population by magisterial districts given below, with a single exception, show an appreciable decrease between the years 1890 and 1900:
| 1900. | 1890. | |
| Broad Run district | 3,309 | 3,463 |
| Jefferson district | 3,106 | 3,307 |
| Leesburg district | 4,299 | 4,246 |
| Lovettsville district | 3,104 | 3,210 |
| Mercer district | 4,010 | 4,570 |
| Mt. Gilead district | 4,120 | 4,478 |
The following incorporated towns for the same period are charged with a corresponding decrease in the number of their inhabitants: