| County | 1990 | 1980 | 1970 | 1960 | 1950 | 1940 | 1930 | 1920 | 1910 | 1900 | 1890 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| DELAWARE | 666,168 | 594,338 | 548,104 | 446,292 | 318,085 | 266,505 | 238,380 | 223,003 | 202,322 | 184,735 | 168,493 |
| Kent | 110,993 | 98,219 | 81,892 | 65,651 | 37,870 | 34,441 | 31,841 | 31,023 | 32,721 | 32,762 | 32,664 |
| New Castle | 441,946 | 398,115 | 385,856 | 307,446 | 218,879 | 179,562 | 161,032 | 148,239 | 123,188 | 109,697 | 97,182 |
| Sussex | 113,229 | 98,004 | 80,356 | 73,195 | 61,336 | 52,502 | 45,507 | 43,741 | 46,413 | 42,276 | 38,647 |
 
| County | 1880 | 1870 | 1860 | 1850 | 1840 | 1830 | 1820 | 1810 | 1800 | 1790 |
|---|---|---|---|---|---|---|---|---|---|---|
| DELAWARE | 146,608 | 125,015 | 112,216 | 91,532 | 78,085 | 76,748 | 72,749 | 72,674 | 64,273 | 59,096 |
| Kent | 32,874 | 29,804 | 27,804 | 22,816 | 19,872 | 19,913 | 20,793 | 20,495 | 19,554 | 18,920 |
| New Castle | 77,716 | 63,515 | 54,797 | 42,780 | 33,120 | 29,720 | 27,899 | 24,429 | 25,361 | 19,688 |
| Sussex | 36,018 | 31,696 | 29,615 | 25,936 | 25,093 | 27,115 | 24,057 | 27,750 | 19,358 | 20,488 |