Arnold is a city in Jefferson County, Missouri, United States, and a suburb of St. Louis. The population was 20,858 at the 2020 United States census.
Arnold Water Tower from I-55 North (color is sky blue since Nov 2015)
Jefferson County, Missouri
Jefferson County is located in the eastern portion of the U.S. state of Missouri. It is a part of the St. Louis Metropolitan Area. As of the 2020 census, the population was 226,739, making it the sixth-most populous county in Missouri. Its county seat is Hillsboro. The county was organized in 1818 and named in honor of former president Thomas Jefferson.
The Jefferson County Courthouse in Hillsboro