Jefferson County, Missouri

Founding: 1819
Parent counties: St. Louis and Ste. Genevieve

Namesake: Thomas Jefferson, U.S. president
Seat: Herculaneum (1818–1839); Hillsboro (1839–)

Land area: 657 square miles

Population (2020): 226,739

Population (historic): 1,835 (1820); 6,928 (1850); 15,380 (1870); 25,712 (1900); 27,563 (1930)

Periods of population growth: pre-1820–1910; 1920–2020

Subdivisions: Ten cities; four villages; seven CDPs; 12 townships

Pre-1940 residences (estimated): 4,518 (5%)
Pre-1940 housing survival rate: 42.5%
Pre-1860 housing survival rate (1940): 12.1%

Farm housing in disrepair (1950): 15.2%

Nonfarm housing in disrepair (1950): 9.6%

Average farmhouse value (1930): $1,391
Average outbuilding value (1930): $860

Average farmhouse size (1940): 4.5 rooms
Number of farms (1920): 2,218
Average farm size (1920): 70.6 acres
Sources of settlement: Germany, Illinois, Ireland, Tennessee, Virginia, and Kentucky

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Hillsboro

Namesake: A traditional name

Founding: 1838 (post office); 1839 (platting as Monticello); 1839 (incorporation)

Population (2020): 3,473

Population (historic): 264 (1890); 233 (1930)

Periods of population growth: pre-1890; 1920–2020
Pre-1940 residences (estimated): 17 (1.8%)

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