Putnam County is a county located in the northwestern part of the U.S. state of Ohio. As of the 2020 census, the population was 34,451. Its county seat is Ottawa. The county was created in 1820 and later organized in 1834. Its name is in honor of Israel Putnam, a colonial officer in the French and Indian War, who served as a general in the American Revolutionary War. The Blanchard River, which passes through the county, was a key transportation route for early European-American settlers.

According to the U.S. Census Bureau, the county has a total area of 484 square miles (1,250 km), of which 483 square miles (1,250 km) is land and 1.8 square miles (4.7 km) (0.4%) is water. The Blanchard River passes through the county.

• Henry County (north)
• Hancock County (east)
• Allen County (south)
• Van Wert County (southwest)
• Paulding County (west)
• Defiance County (northwest)
• Wood County (northeast, at a single point)

Historical population

Census	Pop.	Note	%±
1830	230		—
1840	5,189		2,156.1%
1850	7,221		39.2%
1860	12,808		77.4%
1870	17,081		33.4%
1880	23,713		38.8%
1890	30,188		27.3%
1900	32,525		7.7%
1910	29,972		−7.8%
1920	27,751		−7.4%
1930	25,074		−9.6%
1940	25,016		−0.2%
1950	25,248		0.9%
1960	28,331		12.2%
1970	31,134		9.9%
1980	32,991		6.0%
1990	33,819		2.5%
2000	34,726		2.7%
2010	34,499		−0.7%
2020	34,451		−0.1%
U.S. Decennial Census 1790-1960 1900-1990 1990-2000 2020

As of the census of 2000, there were 34,726 people, 12,200 households, and 9,308 families living in the county. The population density was 72 people per square mile (28 people/km). There were 12,753 housing units at an average density of 26 per square mile (10/km). The racial makeup of the county was 96.26% White, 0.17% Black or African American, 0.15% Native American, 0.18% Asian, 0.01% Pacific Islander, 2.51% from other races, and 0.73% from two or more races. 4.38% of the population were Hispanic or Latino of any race.

There were 12,200 households, out of which 39.20% had children under the age of 18 living with them, 64.90% were married couples living together, 7.40% had a female householder with no husband present, and 23.70% were non-families. 21.30% of all households were made up of individuals, and 10.50% had someone living alone who was 65 years of age or older. The average household size was 2.81 and the average family size was 3.29.

In the county, the population was spread out, with 29.70% under the age of 18, 8.30% from 18 to 24, 28.10% from 25 to 44, 20.60% from 45 to 64, and 13.30% who were 65 years of age or older. The median age was 35 years. For every 100 females there were 98.50 males. For every 100 females age 18 and over, there were 97.00 males.

The median income for a household in the county was $46,426, and the median income for a family was $52,859. Males had a median income of $36,548 versus $23,963 for females. The per capita income for the county was $18,680. About 4.00% of families and 5.60% of the population were below the poverty line, including 6.40% of those under age 18 and 9.80% of those age 65 or over.

As of the 2010 United States Census, there were 34,499 people, 12,872 households, and 9,556 families living in the county. The population density was 71.5 inhabitants per square mile (27.6/km). There were 13,731 housing units at an average density of 28.5 per square mile (11.0/km). The racial makeup of the county was 95.7% white, 0.3% black or African American, 0.2% Asian, 0.2% American Indian, 2.7% from other races, and 0.9% from two or more races. Those of Hispanic or Latino origin made up 5.5% of the population. In terms of ancestry, 65.6% identified as German, 7.8% were Irish, 7.3% were American, 4.7% were English, 2.4% were French, 1.8% were Swiss, 1.7% were Dutch, 1.6% were Italian, 1.4% were Scottish, 1.0% were Welsh, 0.8% were Hungarian and 0.8% were Polish.

Of the 12,872 households, 35.0% had children under the age of 18 living with them, 62.9% were married couples living together, 7.4% had a female householder with no husband present, 25.8% were non-families, and 22.5% of all households were made up of individuals. The average household size was 2.66 and the average family size was 3.13. The median age was 39.0 years.

The median income for a household in the county was $56,573 and the median income for a family was $65,882. Males had a median income of $44,417 versus $33,200 for females. The per capita income for the county was $24,023. About 5.8% of families and 7.1% of the population were below the poverty line, including 9.8% of those under age 18 and 7.0% of those age 65 or over.

Prior to 1940, Putnam County was a Democratic Party county stronghold presidential elections, with James M. Cox in 1920 being the only Democrat to lose it before that year. But starting with the 1940 election, it has become a Republican stronghold. The only 2 Democrats to win the county since then are Harry S. Truman in 1948 and Lyndon B. Johnson in 1964.

Putnam County is known for its strong social conservatism. In November 2023, it gave only 17% of the vote to Ohio Issue 1, which legalized abortion, and 31% to Ohio Issue 2, which legalized recreational marijuana. In both referendums, this was the lowest percentage for any county in Ohio.

United States presidential election results for Putnam County, Ohio

Year	Republican		Democratic		Third party(ies)
	No.	%	No.	%	No.	%
2024	16,576	83.55%	2,996	15.10%	268	1.35%
2020	16,412	82.28%	3,195	16.02%	340	1.70%
2016	14,961	79.34%	2,922	15.50%	974	5.17%
2012	13,721	74.57%	4,318	23.47%	361	1.96%
2008	13,072	69.98%	5,281	28.27%	327	1.75%
2004	14,370	76.24%	4,392	23.30%	87	0.46%
2000	12,837	74.01%	4,063	23.43%	444	2.56%
1996	9,294	57.52%	4,972	30.77%	1,892	11.71%
1992	9,338	54.92%	3,962	23.30%	3,704	21.78%
1988	11,183	73.09%	4,004	26.17%	114	0.75%
1984	11,936	78.26%	3,194	20.94%	121	0.79%
1980	9,752	68.71%	3,742	26.37%	699	4.92%
1976	7,332	57.69%	5,035	39.61%	343	2.70%
1972	8,185	66.32%	3,729	30.21%	428	3.47%
1968	7,188	59.38%	3,530	29.16%	1,387	11.46%
1964	5,221	42.67%	7,014	57.33%	0	0.00%
1960	6,834	53.09%	6,039	46.91%	0	0.00%
1956	8,408	70.38%	3,538	29.62%	0	0.00%
1952	8,398	68.85%	3,799	31.15%	0	0.00%
1948	5,006	49.33%	5,114	50.39%	28	0.28%
1944	8,004	71.79%	3,145	28.21%	0	0.00%
1940	8,946	70.99%	3,655	29.01%	0	0.00%
1936	4,151	33.16%	5,786	46.23%	2,580	20.61%
1932	3,646	30.69%	8,078	68.00%	155	1.30%
1928	5,537	49.20%	5,667	50.36%	50	0.44%
1924	4,377	41.83%	4,795	45.82%	1,293	12.36%
1920	5,157	52.10%	4,673	47.21%	69	0.70%
1916	2,243	33.84%	4,294	64.79%	91	1.37%
1912	1,000	15.60%	4,000	62.40%	1,410	22.00%
1908	2,483	33.17%	4,836	64.61%	166	2.22%
1904	2,853	39.48%	4,145	57.36%	228	3.16%
1900	2,817	35.89%	4,943	62.98%	88	1.12%
1896	2,728	33.68%	5,303	65.48%	68	0.84%
1892	2,314	33.73%	4,177	60.89%	369	5.38%
1888	2,355	34.61%	4,261	62.62%	189	2.78%
1884	2,194	35.11%	4,009	64.15%	46	0.74%
1880	1,851	34.94%	3,417	64.50%	30	0.57%
1876	1,606	33.56%	3,174	66.33%	5	0.10%
1872	1,275	37.22%	2,131	62.20%	20	0.58%
1868	1,184	37.15%	2,003	62.85%	0	0.00%
1864	1,120	39.53%	1,713	60.47%	0	0.00%
1860	1,010	40.48%	1,478	59.24%	7	0.28%
1856	790	41.36%	1,116	58.43%	4	0.21%

The Putnam County Board of Education operates nine separate school districts county-wide.

• Columbus Grove Local School, Putnam County, Ohio
  • St. Anthony's Elementary
• Continental Local School, Putnam County, Ohio
• Fort Jennings Local School District, Putnam County, Ohio
• Kalida Local School District, Putnam County, Ohio
• Leipsic Local School District, Putnam County, Ohio
  • Leipsic St. Mary's Elementary
• McComb Local School District, Hancock County, Ohio (mostly in Hancock County)
• Miller City-New Cleveland Local School District, Putnam County, Ohio
• Ottawa-Glandorf Local School District, Putnam County, Ohio
  • St. Peter and Paul Elementary
  • Loving Care Daycare and Preschool
  • Ottawa-Glandorf Alternative School
• Ottoville Local School District, Putnam County, Ohio
• Pandora-Gilboa Local School, Putnam County, Ohio

Other villages across the county are served by one or more of these districts above in the district's zone area.

• Vaughnsville

• National Register of Historic Places listings in Putnam County, Ohio
• Putnam County, New York

• Marguerite Calvin, Death, Administration, Marriage, and Miscellaneous Notices from the Kalida Venture, Putnam County, Ohio, 1845-1854. Ottawa, OH: Putnam County District Library, 1987.
• Marguerite Calvin, Newspaper Notices from the Kalida Venture, Putnam County, Ohio 1845-1852: A Supplement to Deaths, Administration, Marriage, and Miscellaneous Notices. Ottawa, OH: Putnam County District Library, 1993.
• Marguerite Calvin, Newspaper Notices from the Kalida Sentinel, Putnam County, Ohio, 1861-1866. Ottawa, OH: Putnam County District Library, 1991.
• Marguerite Calvin and David S. Adams, People and Places: Putnam County, Ohio, 1800-1900. Ottawa, OH: M. Calvin, 1981.
• Audrey S. Carroll, Putnam County Pioneer Association: Centennial History, 1873-1973, Putnam County, Ohio. Columbus Grove, OH: Heffner Printing Co., 1973.
• Imogene Elwer, Chronicles of the Past: A History of Putnam County, Ohio. n.c.: n.p., 1990s.
• Delbert L. Gratz, Historical and Genealogical Sketch of the Swiss Mennonites of Allen and Putnam Counties, Ohio. Columbus, OH: Ohio Historical Society, 1940.
• Henry Howe, History of Putnam County, Ohio, 1820-1899. Knightstown, IN: The Bookmark, 1977.
• George D. Kinder, History of Putnam Country, Ohio: Its Peoples, Industries, and Institutions: With Biographical Sketches of Representative Citizens and Genealogical Records of Many of the Old Families. Indianapolis, IN: B.F. Bowen and Co., 1915.
• Putnam County Genealogical Society, Putnam County, Ohio Cemeteries. Ottawa, OH: Putnam County Genealogical Society, 1993.
• Putnam County Historical Society, The Blizzard of 1978 in Putnam County, Ohio. Kalida, OH: Putnam County Historical Society, 1978.
• Putnam County Historical Society, History of Putnam County, Ohio, 1880: Illustrated, Containing Outline Map, Fifteen Farm Maps and a History of the County; Lithographic Views of Buildings — Public and Private; Portraits of Prominent Men; General statistics; Miscellaneous Matters, etc. Mt. Vernon, IN: Windmill Publications, 1995.
• Putnam County Historical Society, Putnam County Pioneer Reminiscences, 1878-1887. Kalida, OH: Putnam County Historical Society, 1981.
• Daniel W. Seitz and O.C. Talbot, The Putnam County Atlas, 1895: Containing Sectional Outline Maps of the County...Farm Maps of the Fifteen Townships...Together with Maps of All the Towns Reduced to Single Page Size... Ottawa, OH: D.W. Seitz and O.C. Talbot, 1895.
• Mary L. Sheeley, Putnam County, Ohio One-Room Schools. Kalida, OH: Putnam County Historical Society, 1985.
• Marjorie Waterfield, The Ledger Tells the Story, 1811-1879: The History of the Irwin family of Putnam County, Ohio. Bowling Green, OH: M. Waterfield, 1997.
• A Portrait and Biographical Record of Allen and Putnam Counties, Ohio: Containing Biographical Sketches of Many Prominent and Representative Citizens, Together with Biographies and Portraits of All the Presidents of the United States, and Biographies of the Governors of Ohio. Chicago: A.W. Bowen & Company, 1896.

• Official Putnam County website

41°01′N 84°08′W / 41.02°N 84.13°W / 41.02; -84.13