Seneca County, Ohio

Founding: 1824 (declared in 1820)
Parent county: Unorganized territory

Namesake: The Seneca tribe
Seat: Tiffin (1824–)

Land area: 551 square miles

Population (2020): 55,069

Population (historic): 5,159 (1830); 30,868 (1860); 41,163 (1900); 47,941 (1930)

Periods of population growth: 1820–1860; 1870–1980

Subdivisions: Two cities; six villages; seven CDPs; 15 townships

National Register listings: 45

Pre-1940 residences (estimated): 8,857 (36.9%)
Pre-1940 housing survival rate: 71.7%
Pre-1860 housing survival rate (1940): 22.4%

Farm housing in disrepair (1950): 3.4%

Nonfarm housing in disrepair (1950): 5%
Average farmhouse value (1930): $2,021
Average outbuilding value (1930): $2,109

Average farmhouse size (1940): 7.5 rooms
Number of farms (1920): 3,113
Average farm size (1920): 89.9 acres
Sources of settlement: Pennsylvania, Germany, Maryland, and New York
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Tiffin

Namesake: Edward Tiffin, first Ohio governor

Founding: 1821 (platting); 1825 (post office); 1835 (incorporation)

Population (2020): 17,953

Population (historic): 248 (1830); 3,992 (1860); 10,989 (1900); 16,428 (1930)

Periods of population growth: 1821–1930; 1940–1970

Pre-1940 residences (estimated): 2,872 (37.8%)
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Outstanding Buildings

1. *Clay Holtz House (1868). 5325 North State Route 101. Adams. Italianate.
2. *Thomas Dunnage Farm (c. 1860). 7618 North Township Road 32. Adams.
3. St. Nicholas Catholic Church (1887–1890). 8981 West County Road 6. Big Spring. Romanesque.
4. Sts. Peter and Paul Catholic Church (1880–1881). 11125 West Township Road 95. Big Spring. Romanesque.
5. *Benjamin Huddle Log House (c. 1835). 7240 South County Road 43. Bloom.
6. *Noah Rinehart House (c. 1845). 7245 South County Road 43. Bloom.
7. *Simon Koller House (c. 1845). 7566 East Township Road 163. Bloom.
8. *Thomas Bagby House (1862). 1822 South County Road 19. Clinton.
9. *Call Farm (c.1850). 2373 East State Route 18. Clinton. Greek Revival.
10. *George Kalbfleisch Estate (1925–1926). 2721 North State Route 53. Clinton. Tudor Revival.
11. *Ezra Baker House (1849). 2721 North State Route 53. Clinton. Greek Revival.
12. *Michael Bastian House (c. 1845). 347 North Township Road 194. Clinton. Greek Revival.
13. *Henry Ladd House (c. 1845). State Route 67. Eden. Greek Revival. Razed.
14. School (c. 1890). 3998 West Township Road 112. Hopewell. Romanesque.
15. John Baltzell Farm (1856). 2786 South State Route 53. Hopewell. Greek Revival/Italianate.
16. *Elisha Umsted Log House (c. 1840). 481 East County Road 38. Pleasant. Razed.
17. *Ephraim Umsted Farm (c. 1865). 481 East County Road 38. Pleasant. Italianate.
18. *William White House (1843). 2460 North County Road 27. Reed. Greek Revival. Razed.
19. Assumption Catholic Church (1907–1908). 1931 North County Road 29. Reed. Gothic Revival.
20. *Timothy Weed Farm (c. 1855). 11962 East Township Road 124. Reed. Greek Revival.
21. *Omar Chapel (1843). 408 South State Route 4. Reed. Greek Revival.
22. *Brown House (c. 1845). 7251 East Township Road 8. Scipio. Greek Revival.
23. *George Christlip House (c. 1855). West County Road 6. Seneca. Greek Revival.
24. Nathan Butz House (c. 1875). 3266 North County Road 27. Thompson. Second Empire. Razed.
25. *George Heter House (1849). 8531 North County Road 29. Thompson. Greek Revival.
26. *St. Michael Catholic Church (1884). 16223 East County Road 46. Thompson. Gothic Revival.
27. *Jacob Miller House (1850). 5191 North Township Road 81. Thompson. Greek Revival.
28. *Burgner House (1847–1849). 8627 North Township Road 81. Thompson. Razed.