Mercer County, Ohio

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

Namesake: Hugh Mercer, Continental Army general
Seat: St. Marys (1824–1839); Celina (1839–)

Land area: 462 square miles

Population (2020): 42,528

Population (historic): 1,110 (1830); 14,104 (1860); 21,808 (1880); 28,021 (1900); 25,096 (1930)

Periods of population growth: 1820–1840; 1850–1900; 1930–2000; 2010s

Subdivisions: One city; seven villages; 14 townships

Pre-1940 residences (estimated): 3,578 (20.3%)
Pre-1940 housing survival rate: 56.8%
Pre-1860 housing survival rate (1940): 3.6%

Farm housing in disrepair (1950): 3.4%

Nonfarm housing in disrepair (1950): 3.5%
Average farmhouse value (1930): $1,393
Average outbuilding value (1930): $1,642

Number of farms (1920): 3,040
Average farm size (1920): 77.8 acres
Sources of settlement: Germany and Pennsylvania
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Celina

Namesake: Salina, New York

Founding: 1834 (platting); 1840 (post office); 1860 (incorporation)

Population (2020): 10,935

Population (historic): 222 (1850); 1,346 (1880); 2,815 (1900); 4,664 (1930)

Periods of population growth: 1834–2020
Pre-1940 residences (estimated): 657 (13.3%)
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Outstanding Buildings

1. Martin Winkler Farm (c. 1885). 12561 Wabash Road. Black Creek. Italianate.
2. George Dellinger Log House (1852). 799 Winkler Road. Black Creek.
3. Joseph Speck Farm (1872). 3459 State Route 119. Granville. Razed.
4. Henry Aufderhaar Log House (c. 1870). 3066 Carmel Church Road. Jefferson. Razed.
5. Maria Stein Convent (1892/1910). 2291 St. John's Road. Marion. Gothic Revival.
6. Bernard Knapke Farm (1874). 2570 St. John's Road. Marion.
7. Joseph Ungruhn Farm (1882). 6926 State Route 119. Marion.
8. St. Aloysius Catholic Church (1875–1878). 6032 State Route 274. Marion. Romanesque.
9. Henry Grieshop Farm (c. 1870). 8739 State Route 274. Marion.
10. St. Charles Seminary (1919–1925). 2860 US Highway 127. Marion. Gothic Revival.
11. St. Peter Catholic Church (1904–1906). 3512 St. Peter Road. Recovery. Gothic Revival.
12. Philo Wallischeck Farm (1867). 80 Zehringer Road. Recovery. Razed.
13. Isham Robbins Farm (1884). 11020 Gallman Road. Union. Italianate.

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