Marion County is a county located in the state of Ohio, United States. According to the 2010 census, it has a population of 66,501, which is an increase of 0.4% from 66,217 in 2000. Its county seat is the city of Marion and is named for General Francis "The Swamp Fox" Marion, an officer in the Revolutionary War.

The Marion Micropolitan Statistical Area includes all of Marion County.

According to the 2010 census, the county has a total area of 404.11 square miles (1,046.6 km²), of which 403.76 square miles (1,045.7 km²) (or 99.91%) is land and 0.35 square miles (0.91 km²) (or 0.09%) is water.

As of the census of 2000, there were 66,217 people, 24,578 households, and 17,253 families residing in the county. The population density was 164 people per square mile (63/km²). There were 26,298 housing units at an average density of 65 per square mile (25/km²). The racial makeup of the county was 92.10% White, 5.75% Black or African American, 0.19% Native American, 0.52% Asian, 0.01% Pacific Islander, 0.49% from other races, and 0.95% from two or more races. 1.09% of the population were Hispanic or Latino of any race.

Ohio (ⁱ/oʊˈhaɪ.oʊ/) is a state in the Midwestern United States. Ohio is the 34th most extensive, the 7th most populous, and the 10th most densely populated of the 50 United States. The state's capital and largest city is Columbus.

The name "Ohio" originated from Iroquois word ohi-yo’, meaning "great river". The state, originally partitioned from the Northwest Territory, was admitted to the Union as the 17th state (and the first under the Northwest Ordinance) on March 1, 1803. Although there are conflicting narratives regarding the origin of the nickname, Ohio is historically known as the "Buckeye State" (relating to the Ohio buckeye tree) and Ohioans are also known as "Buckeyes".

The government of Ohio is composed of the executive branch, led by the Governor; the legislative branch, which comprises the Ohio General Assembly; and the judicial branch, which is led by the Supreme Court. Currently, Ohio occupies 18 seats in the United States House of Representatives. Ohio is known for its status as both a swing state and a bellwether in national elections.

Marion County is a county located in the U.S. state of Oregon. It was originally named the Champooick District, after Champoeg, a meeting place on the Willamette River. On September 3, 1849, the territorial legislature renamed it in honor of Francis Marion, a Continental Army general of the American Revolutionary War. The population was 315,335 at the 2010 census. The county seat is Salem.

Marion County is part of the Salem Metropolitan Statistical Area.

Marion County was created on July 5, 1843, one of the original four districts of the Oregon territory along with Twality (later Washington), Clackamas, and Yamhill counties. The four districts were redesignated as counties in 1845.

Originally, this political entity stretched southward to the California border and eastward to the Rocky Mountains. With the creation of Wasco, Linn, Polk, and other counties, its area was reduced in size. Marion County's present geographical boundaries were established in 1856.

In 1849, Salem was designated the county seat. The territorial capital was moved from Oregon City to Salem in 1852. The ensuing controversy over the location of the capital was settled in 1864 when Salem was confirmed as the state capital.