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

National Register listings: 15

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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Outstanding Buildings

1. St. John's Lutheran Church (1929). 3517 Jefferson County Boulevard. Arnold. Gothic Revival.
2. John Frederitzi House (c. 1855). 1917 Old LeMay Ferry Road. Arnold.
3. Log House (c. 1840). 7007 3B Road. Big River.
4. John Thomas House (c. 1870). 2401 Stone House Road. Big River. Italianate.
5. *The Cedars / Benjamin O'Fallon House (c. 1835). 200 Liguori Drive. Imperial. Razed.
6. James O'Fallon House (1860). 1901 Parkton Way. Imperial. Gothic Revival.
7. *John Herrington Log House (c. 1840). US Highway 61, north of State Route Z. Joachim. Razed.
8. *David Bryant House (c. 1855). Dunklin Drive, north of Herculaneum. Joachim. Gothic Revival. Razed.
9. *Greystone / James Dunklin House (c. 1855). 900 Evergreen Hill Lane. Joachim. Gothic Revival.
10. *Alexander Ziegler House (c. 1845). 459 Landmark Manor Drive. Joachim. Greek Revival.
11. House (c. 1865). 2971 Road P. Joachim.
12. John Canepa House (1883). 1220 Canepa Road. Plattin. Italianate.
13. Baker House (c. 1870). 1287 Canepa Road. Plattin.
14. James McCormack Farm (1836). Harness Road, at Charter Church Road. Plattin. Razed.
15. Bailey Log House (1821/1842). 1600 Kessler Lane. Plattin. Razed.
16. Thomas Donnell Farm (c. 1855). 2826 Plattin Road. Plattin. Greek Revival.
17. *Selma Hall / Ferdinand Kennett Estate (1854). 4 Selma Farm Lane. Plattin. Renaissance Revival.
18. *John Brook Log House (1826). 4727 US Highway 61. Plattin. Greek Revival. Razed.
19. St. Joseph's Ursuline Novitiate (1936). 210 Glennon Heights Road. Riverview. Romanesque.
20. Valle Log House. 4090 Valle's Mines School Road. Valle.