DeKalb County, Illinois

Founding: 1837
Parent county: Kane

Namesake: Johann de Kalb, Continental Army general
Seat: Sycamore (1837–)

Land area: 631 square miles

Population (2020): 100,420

Population (historic): 1,697 (1840); 19,086 (1860); 26,768 (1880); 31,756 (1900); 32,644 (1930)

Periods of population growth: pre-1840–1910; 1920–2010

Subdivisions: Four cities; one town; seven villages; 19 townships

National Register listings: 18

Pre-1940 residences (estimated): 7,784 (18.9%)
Pre-1940 housing survival rate: 74%
Pre-1860 housing survival rate (1940): 11%

Farm housing in disrepair (1950): 6.7%

Nonfarm housing in disrepair (1950): 4.6%

Average farmhouse value (1930): $2,642
Average outbuilding value (1930): $3,966

Average farmhouse size (1940): 7.5 rooms
Number of farms (1920): 2,400
Average farm size (1920): 147.4 acres
Sources of settlement: New York, Pennsylvania, Germany, Sweden, Ireland, England, and Canada
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Sycamore

Namesake: Uncertain—presumably a sycamore grove near the city site

Founding: 1837 (platting); 1840 (post office); 1859 (incorporation)

Population (2020): 18,577

Population (historic): 338 (1850); 1,967 (1870); 2,987 (1890); 3,926 (1910); 4,021 (1930)

Periods of population growth: pre-1850–1880; 1890–1910; 1920–2020
Pre-1940 residences (estimated): 1,108 (15.9%)
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Outstanding Buildings

1. Porter Coolidge House (1875). 14415 Bethany Road. Cortland. Italianate.
2. *Joseph Glidden House (1861). 921 West Lincoln Highway. DeKalb. Italianate.
3. *Matthew Nisbet Farm (1848–1863). 3719 Suydam Road. Paw Paw. Greek Revival.
4. *Henry Roth Farm (c. 1855). 12971 Somonauk Road. Pierce. Greek Revival.
5. David Harmon Farm (c. 1850). 1709 Somonauk Road. Somonauk. Greek Revival.
6. *Stephen Wright Farm (c. 1850). 2400 Suydam Road. Somonauk. Greek Revival.
7. *James Gibson House (c. 1865). 26483 Schafer Road. South Grove. Italianate.
8. Ephraim Hall Farm (c. 1870). 29245 State Route 23. Sycamore. Italianate.
9. Almon Parke Farm (c. 1880). 28929 State Route 23. Sycamore. Italianate.