Jefferson County, New York

Founding: 1805
Parent county: Oneida
Namesake: Thomas Jefferson, U.S. president
Seat: Watertown (1805–)
Land area: 1,269 square miles
Population (2020): 116,721
Population (historic): 15,140 (1810); 60,984 (1840); 65,415 (1870); 76,748 (1900); 83,574 (1930)
Periods of population growth: pre-1810–1860; 1870–1970; 1980–2020
Subdivisions: One city; 19 villages; 21 CDPs; 22 towns
Pre-1940 residences (estimated): 19,824 (33.1%)
Pre-1940 housing survival rate: 73.4%
Pre-1860 housing survival rate (1940): 26.7%

Farm housing in disrepair (1950): 9.7%

Nonfarm housing in disrepair (1950): 5.9%

Average farmhouse value (1930): $1,766
Average outbuilding value (1930): $2,190
Average farmhouse size (1940): 8.3 rooms
Number of farms (1920): 5,151
Average farm size (1920): 88 acres
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Watertown

 
Namesake: A reference to the Black River, which bisects the city
Founding: 1800 (founding); 1804 (post office); 1816 (incorporation)
Population (2020): 24,685
Population (historic): 9,336 (1870); 14,725 (1890); 26,730 (1910); 32,205 (1930)
Periods of population growth: pre-1870–1950; 1980s; 2000s
Pre-1940 residences (estimated): 6,989 (53%)
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