| | Population, April 1, 1990 | Population, April 1, 2000 | Numeric Population Change, 1990 to 2000 | Percent Population Change, 1990 to 2000 | Land Area (square miles), 2000 | Persons Per Square Mile, 1990 | Persons Per Square Mile, 2000 |
|
| United States | 248,709,873 | 281,421,906 | 32,712,033 | 13.2% | 3,537,438.4 | 70.3 | 79.6 |
| Appalachian Region | 21,727,579 | 23,642,578 | 1,914,999 | 8.8% | 204,812.1 | 106.1 | 115.4 |
| Maryland | 4,781,468 | 5,296,486 | 515,018 | 10.8% | 9,773.8 | 489.2 | 541.9 |
| Appalachian Maryland | 224,477 | 236,699 | 12,222 | 5.4% | 1,531.5 | 146.6 | 154.6 |
|
| County |
| Allegany | 74,946 | 74,930 | -16 | 0.0% | 425.4 | 176.2 | 176.1 |
| Garrett | 28,138 | 29,846 | 1,708 | 6.1% | 648.0 | 43.4 | 46.1 |
| Washington | 121,393 | 131,923 | 10,530 | 8.7% | 458.1 | 264.9 | 288.0 |
