Marshall County is a county in the U.S. state of Indiana. The 2020 census recorded the population at 46,095. The county seat (and only city) is Plymouth.

The Indiana State Legislature passed an omnibus county bill on February 7, 1835, that authorized the creation of thirteen counties in northeast Indiana, including Marshall. It was named for U.S. Chief Justice John Marshall, who died in 1835. The government of the county was organized in 1836, during the early years of settlement and before the forced removal of the Potawatomi people in 1838. The first settlers had arrived in the county in 1835; they arrived as a result of the end of the Black Hawk War as well as the completion of the Erie Canal. They consisted primarily of settlers from New England, "Yankees" descended from the English Puritans who settled New England in the colonial era. They were mainly members of the Congregational Church, although due to the Second Great Awakening many of them had converted to Methodism and some had become Baptists before migrating to the new area. As a result of this heritage, some place names in Marshall County are named after places in New England, such as Plymouth, which is named after Plymouth, Massachusetts, the site where the Mayflower landed in 1620.

The low, rolling hills of Marshall County are completely devoted to agriculture where possible (significant drainages are wooded). The highest points on the terrain are three approximately equal swells (900 ft; 270 m ASL) along the south border line with Fulton County, 1.4 miles (2.3 km) NW of Richland Center.

Marshall County contains three significant bodies of water: Lake of the Woods (NE portion); Lake Maxinkuckee (SW portion); and part of Koontz Lake (NW portion). The Yellow River flows through northern, central, and western portions of Marshall County, past Plymouth; the Tippecanoe River flows southwesterly through the SE part of the county.

According to the 2010 census, Marshall County has a total area of 449.74 square miles (1,164.8 km), of which 443.63 square miles (1,149.0 km) (or 98.64%) is land and 6.11 square miles (15.8 km) (or 1.36%) is water.

• Menominee Wetland Conservation Area (W of Plymouth)
• Potawatomi Wildlife Park (on W bank of Tippecanoe River in SE county)

• Koontz Lake (partial)

Plymouth, Indiana
Climate chart (explanation)
J F M A M J J A S O N D     2.2     32 16     1.9     38 20     2.9     49 29     4     62 39     4.3     74 49     4.5     83 58     3.7     86 62     3.4     84 60     3.6     77 53     3.2     64 42     3.2     50 32     2.8     37 22 █ Average max. and min. temperatures in °F █ Precipitation totals in inches Source: The Weather Channel
Metric conversion J F M A M J J A S O N D     55     0 −9     47     3 −7     72     9 −2     101     17 4     108     23 9     114     28 14     95     30 17     85     29 16     91     25 12     81     18 6     81     10 0     71     3 −6 █ Average max. and min. temperatures in °C █ Precipitation totals in mm

In recent years, average temperatures in Plymouth have ranged from a low of 16 °F (−9 °C) in January to a high of 86 °F (30 °C) in July, although a record low of −25 °F (−32 °C) was recorded in January 1985 and a record high of 109 °F (43 °C) was recorded in July 1936. Average monthly precipitation ranged from 1.86 inches (47 mm) in February to 4.48 inches (114 mm) in June.

The county government is a constitutional body, and is granted specific powers by the Constitution of Indiana, and by the Indiana Code.

County council: The legislative branch of the county government; controls spending and revenue collection in the county. Representatives are elected to four-year terms from county districts. They set salaries, the annual budget, and special spending. The council has limited authority to impose local taxes, in the form of an income and property tax that is subject to state level approval, excise taxes, and service taxes.

Board of commissioners: The executive body of the county; commissioners are elected county-wide, to staggered four-year terms. One commissioner serves as president. The commissioners execute acts legislated by the council, collect revenue, and manage the functions of the county government.

Current commissioners: Stan Klotz, Mike Burroughs, Kevin Overmyer (as of July 2020)

Court: The county maintains a small claims court that handles civil cases. The judge on the court is elected to a term of four years and must be a member of the Indiana Bar Association. The judge is assisted by a constable who is also elected to a four-year term. In some cases, court decisions can be appealed to the state level circuit court.

County Officials: The county has other elected offices, including sheriff, coroner, auditor, treasurer, recorder, surveyor, and circuit court clerk. Officials are elected to four-year terms. Members elected to county government positions are required to declare party affiliations and to be residents of the county.

Marshall County is part of Indiana's 2nd congressional district and is currently represented by Rudy Yakym in the United States Congress. It is also part of Indiana Senate districts 5 and 9 and Indiana House of Representatives districts 17 and 23.

United States presidential election results for Marshall County, Indiana

Year	Republican		Democratic		Third party(ies)
	No.	%	No.	%	No.	%
2024	13,837	70.54%	5,356	27.30%	423	2.16%
2020	13,844	69.38%	5,712	28.63%	397	1.99%
2016	12,288	67.36%	4,798	26.30%	1,155	6.33%
2012	11,260	63.25%	6,137	34.48%	404	2.27%
2008	10,406	56.03%	7,889	42.48%	276	1.49%
2004	12,074	67.78%	5,593	31.40%	147	0.83%
2000	10,266	63.57%	5,541	34.31%	343	2.12%
1996	8,158	52.84%	5,486	35.53%	1,796	11.63%
1992	8,048	48.58%	4,912	29.65%	3,607	21.77%
1988	10,490	65.41%	5,488	34.22%	60	0.37%
1984	11,100	68.76%	4,931	30.54%	113	0.70%
1980	10,209	62.21%	5,113	31.16%	1,089	6.64%
1976	9,707	59.16%	6,424	39.15%	277	1.69%
1972	11,908	73.02%	4,349	26.67%	51	0.31%
1968	9,290	56.67%	5,385	32.85%	1,719	10.49%
1964	7,895	48.10%	8,397	51.15%	123	0.75%
1960	10,460	62.47%	6,210	37.09%	74	0.44%
1956	10,504	65.72%	5,398	33.78%	80	0.50%
1952	9,990	63.12%	5,538	34.99%	300	1.90%
1948	7,873	56.97%	5,661	40.97%	285	2.06%
1944	8,225	59.88%	5,254	38.25%	257	1.87%
1940	7,718	56.41%	5,852	42.77%	111	0.81%
1936	6,118	47.17%	6,651	51.28%	202	1.56%
1932	4,943	39.84%	7,212	58.13%	252	2.03%
1928	6,738	60.24%	4,377	39.13%	70	0.63%
1924	5,354	53.22%	4,277	42.51%	429	4.26%
1920	5,708	53.64%	4,631	43.52%	303	2.85%
1916	2,855	44.64%	3,221	50.36%	320	5.00%
1912	1,196	20.21%	2,859	48.31%	1,863	31.48%
1908	2,947	45.31%	3,287	50.54%	270	4.15%
1904	3,001	48.39%	2,878	46.40%	323	5.21%
1900	2,947	45.12%	3,449	52.81%	135	2.07%
1896	2,938	44.45%	3,588	54.29%	83	1.26%
1892	2,558	43.41%	3,113	52.83%	222	3.77%
1888	2,582	43.70%	3,188	53.96%	138	2.34%

Historical population

Census	Pop.	Note	%±
1840	1,651		—
1850	5,348		223.9%
1860	12,722		137.9%
1870	20,211		58.9%
1880	23,414		15.8%
1890	23,818		1.7%
1900	25,119		5.5%
1910	24,175		−3.8%
1920	23,744		−1.8%
1930	25,077		5.6%
1940	25,935		3.4%
1950	29,468		13.6%
1960	32,443		10.1%
1970	34,986		7.8%
1980	39,155		11.9%
1990	42,182		7.7%
2000	45,128		7.0%
2010	47,051		4.3%
2020	46,095		−2.0%
2023 (est.)	46,352		0.6%
US Decennial Census 1790-1960 1900-1990 1990-2000 2010

As of the 2010 United States Census, there were 47,051 people, 17,406 households, and 12,516 families in the county. The population density was 106.1 inhabitants per square mile (41.0/km). There were 19,845 housing units at an average density of 44.7 per square mile (17.3/km). The racial makeup of the county was 93.5% white, 0.5% black or African American, 0.5% Asian, 0.2% American Indian, 3.8% from other races, and 1.5% from two or more races. Those of Hispanic or Latino origin made up 8.4% of the population. In terms of ancestry, 35.4% were German, 11.2% were Irish, 9.4% were American, and 8.5% were English.

Of the 17,406 households, 35.2% had children under the age of 18 living with them, 57.2% were married couples living together, 9.9% had a female householder with no husband present, 28.1% were non-families, and 24.1% of all households were made up of individuals. The average household size was 2.66 and the average family size was 3.15. The median age was 38.4 years.

The median income for a household in the county was $47,697 and the median income for a family was $58,017. Males had a median income of $43,732 versus $30,033 for females. The per capita income for the county was $22,493. About 8.7% of families and 12.2% of the population were below the poverty line, including 17.1% of those under age 18 and 10.4% of those age 65 or over.

• National Register of Historic Places listings in Marshall County, Indiana

41°20′N 86°16′W / 41.33°N 86.26°W / 41.33; -86.26