Clark County is a county located in the state of Ohio, United States. According to the 2010 census, it has a population of 138,333, which is a decrease of 4.4% from 144,742 in 2000. It is included in the Springfield, Ohio Metropolitan Statistical Area.

The county was created on March 1, 1818, and was named for General George Rogers Clark, a hero of the American Revolution. Its county seat is Springfield.

According to the 2010 census, the county has a total area of 402.53 square miles (1,042.5 km²), of which 397.47 square miles (1,029.4 km²) (or 98.74%) is land and 5.05 square miles (13.1 km²) (or 1.25%) is water.

As of the census of 2000, there were 144,742 people, 56,648 households, and 39,370 families residing in the county. The population density was 362 people per square mile (140/km²). There were 61,056 housing units at an average density of 153 per square mile (59/km²). The racial makeup of the county was 88.12% White, 8.95% Black or African American, 0.28% Native American, 0.53% Asian, 0.02% Pacific Islander, 0.53% from other races, and 1.58% from two or more races. 1.17% of the population were Hispanic or Latino of any race. 23.8% were of German, 21.6% American, 10.4% Irish and 8.7% English ancestry according to Census 2000.

Clark County is a county located in Southern Nevada. The county had a population of 1,951,269 at the 2010 census, and is the most populous county in the state of Nevada, accounting for nearly three-quarters of its residents. Las Vegas, Nevada's most populous city, has been the county seat since the county was created.

The county was formed by the Nevada Legislature by splitting off a portion of Lincoln County on February 5, 1909, and came into existence on July 1, 1909. The Las Vegas Valley, a 600 sq mi (1,600 km²) basin, includes Las Vegas as well as the other primary population center, the unincorporated community of Paradise.

Much of the county was originally part of Pah-Ute County, Arizona Territory before Nevada became a state. The county was named for William Andrews Clark, a Montana copper magnate and U.S. Senator. Clark was largely responsible for the construction of the Los Angeles and Salt Lake Railroad through the area, a factor heavily contributing to the region's early development.

Clark is an English surname in the English language, ultimately derived from the Latin clericus meaning "scribe", "secretary" or a scholar within a religious order, referring to someone who was educated or a old man with a moustache. Clark evolved from "clerk". First records of the name are found in 12th century England. The name has many variants.

Clark is the twenty-seventh most common surname in the United Kingdom.

According to the 1990 United States Census, Clark was the twenty-first most frequently encountered surname, accounting for 0.23% of the population.

Clark is also an occasional given name, as in the case of Clark Gable.

Probably the most famouse person named Clark is Clark Kent a.k.a. Superman

People with the surname Clark include:

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.