Jefferson County, Illinois

Founding: 1819
Parent counties: Edwards and White

Namesake: Thomas Jefferson, U.S. president
Seat: Mount Vernon (1819–)

Land area: 571 square miles

Population (2020): 37,113

Population (historic): 691 (1820); 8,109 (1850); 17,864 (1870); 28,133 (1900); 31,034 (1930)

Periods of population growth: pre-1820–1910; 1920–1950; 1970–2000

Subdivisions: Two cities; seven villages; one CDP; 16 townships

National Register listings: Two

Pre-1940 residences (estimated): 2,404 (14.2%)
Pre-1940 housing survival rate: 29.7%
Pre-1860 housing survival rate (1940): 5.2%

Farm housing in disrepair (1950): 9.7%

Nonfarm housing in disrepair (1950): 12%

Average farmhouse value (1930): $729
Average outbuilding value (1930): $370

Average farmhouse size (1940): 4.7 rooms
Number of farms (1920): 3,592
Average farm size (1920): 79.5 acres
Sources of settlement: Tennessee, Kentucky, Indiana, and Ohio
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Mount Vernon

Namesake: Mount Vernon, George Washington's estate

Founding: 1817 (platting); 1829 (post office); 1837 (incorporation)

Population (2020): 14,600

Population (historic): 707 (1860); 2,324 (1880); 5,216 (1900); 12,375 (1930)

Periods of population growth: pre-1860–1950; 1960–1980
Pre-1940 residences (estimated): 1,410 (18.4%)
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Outstanding Buildings

1. *Charles Judd Farm (1881). 20618 Ina Road. Moore's Prairie. Italianate/Eastlake.
2. *Tazewell Tanner House (c. 1870). 2023 Richview Road. Shiloh. Gothic Revival.