Mercer County, Illinois

Founding: 1835 (declared in 1825)
Parent county: Unorganized territory

Namesake: Hugh Mercer, Continental Army general
Seat: Millersburg (1835–1857); Aledo (1857–)

Land area: 561 square miles

Population (2020): 15,699

Population (historic): 2,352 (1840); 15,042 (1860); 19,502 (1880); 20,945 (1900); 16,641 (1930)

Periods of population growth: 1830–1880; 1890s; 1930s; 1960–1980

Subdivisions: Three cities; nine villages; 15 townships

National Register listings: 13

Pre-1940 residences (estimated): 2,941 (39.7%)
Pre-1940 housing survival rate: 55.2%
Pre-1860 housing survival rate (1940): 8.2%

Farm housing in disrepair (1950): 5.1%

Nonfarm housing in disrepair (1950): 5.9%

Average farmhouse value (1930): $2,738
Average outbuilding value (1930): $2,795

Average farmhouse size (1940): 6.7 rooms
Number of farms (1920): 2,022
Average farm size (1920): 129.7 acres
Sources of settlement: Pennsylvania, Ohio, Sweden, Indiana, and Ireland
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Aledo

Namesake: Unknown

Founding: 1856 (platting); 1856 (post office); 1863 (incorporation)

Population (2020): 3,633

Population (historic): 563 (1860); 1,492 (1880); 2,081 (1900); 2,203 (1930)

Periods of population growth: 1856–1920; 1930–1980; 2000s
Pre-1940 residences (estimated): 584 (34.6%)
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Outstanding Buildings

1. *James Kimel Farm (c. 1865). 656 State Route 94. Mercer. Italianate.
2. *Verdurette / William Drury Farm (1855/1909). 663 65th Road. New Boston. Gothic Revival.
3. *James Thompson House (1867). 804 North Street. New Boston. Italianate.
4. *Robert Candor House (1872). 436 160th Road. Ohio Grove. Italianate.
5. *Pope Creek Presbyterian Church (1849). 160th Road, north of 40th Road. Ohio Grove. Greek Revival.
6. *Graham Lee Farm (c. 1870). 1631 State Route 94. Perryton. Italianate. Razed.
7. *Edward Farwell Farm (c. 1850). 1594 US Highway 67. Preemption. Greek Revival.