High Quality Content by WIKIPEDIA articles! Osage County is a county located in the U.S. state of Missouri. The county was named for the Osage River. As of 2000, the population was 13,062. Its county seat is Linn. The center of population of Missouri is located in Osage County, in the city of Westphalia. Osage County is part of the Jefferson City, Missouri, Metropolitan Statistical Area. Its geography and the founding of Westphalia Vineyards links it to the Missouri Rhineland, extending along the Missouri River valley to the western edges of the St. Louis metropolitan area. Although started only in 2005, Westphalia Vineyards won the gold medal in the National Norton Festival Wine Competition in St. Louis in 2007 for the top-rated wine from the Norton grape.