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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