Warren County is a county located in the U.S. state of Missouri. Warren County is part of the St. Louis Metro Area and is located west of the city on the north side of the Missouri River. As of 2008, the population was estimated to be 31,214. Its county seat is Warrenton. The county was organized on January 5, 1833, and is named for General Joseph Warren, who died in the Battle of Bunker Hill during the American Revolutionary War.

Warren County is traversed by Route 94, called the "Missouri Weinstrasse" because of the many vineyards from Marthasville east into St. Charles County. Warren County is part of the Missouri Rhineland, with award-winning wineries located on both sides of the Missouri River.

According to the 2000 census, the county has a total area of 437.74 square miles (1,133.7 km²), of which 431.31 square miles (1,117.1 km²) (or 98.53%) is land and 6.43 square miles (16.7 km²) (or 1.47%) is water.

As of the census of 2000, there were 24,525 people, 9,185 households, and 6,888 families residing in the county. The population density was 57 people per square mile (22/km²). There were 11,046 housing units at an average density of 26 per square mile (10/km²). The racial makeup of the county was 95.89% White, 1.94% Black or African American, 0.45% Native American, 0.24% Asian, 0.02% Pacific Islander, 0.44% from other races, and 1.02% from two or more races. Approximately 1.28% of the population were Hispanic or Latino of any race. Among the major ancestries reported in Warren County were 41.4% German, 13.8% American, 10.2% Irish and 7.0% English ancestry according to Census 2000.

Missouri (ⁱ/mɨˈzʊəri/) (nickname The Show Me State) is a U.S. state located in the Midwestern United States, bordered by Iowa, Illinois, Kentucky, Tennessee, Arkansas, Oklahoma, Kansas and Nebraska. Missouri is the 21st most extensive and the 18th most populous of the 50 United States. Missouri comprises 114 counties and the independent city of St. Louis. The four largest urban areas are St. Louis, Kansas City, Springfield, and Columbia. Missouri's capital is Jefferson City. The land that is now Missouri was acquired from France as part of the Louisiana Purchase and became known as the Missouri Territory. Part of the Territory was admitted into the union as the 24th state on August 10, 1821.

Missouri generally mirrors the demographic, economic and political makeup of America and has long been considered a political bellwether state. With the exceptions of the Presidential elections of 1956 and 2008, Missouri's results have accurately predicted the next President of the United States in every election since 1904. It has both Midwestern and Southern cultural influences, reflecting its history as a border state. It is also a transition between the Eastern and Western United States, as St. Louis is often called the "western-most Eastern city" and Kansas City the "eastern-most Western city". Missouri's geography is highly varied. The northern part of the state lies in dissected till plains while the southern part lies in the Ozark Mountains (a dissected plateau), with the Missouri River dividing the two. The state lies at the intersection of the three greatest rivers of North America, with the confluence of the Mississippi and Missouri Rivers near St. Louis, and the confluence of the Ohio River with the Mississippi north of the Bootheel. The starting points of the Pony Express Trail and Oregon Trail were both in Missouri. The mean center of United States population as of the 2010 Census is at the town of Plato in Texas County, Missouri.

Warren County is the name of fourteen counties in the USA. They are named after General Joseph Warren, who was killed in the Battle of Bunker Hill in the American Revolutionary War: