Jefferson County is a county located in the U.S. state of Missouri. As of the most recent data available, the county has a population of approximately 198,099 people, with a population density of about 301.52 persons per square mile.
The county spans a total land area of 657.00 square miles (1,702.00 square kilometers). The administrative center and county seat is Hillsboro, which often serves as a hub for local governance and services. The largest city within the county by population is Arnold.
Geographically, Jefferson County experiences varied elevations, with its highest point at High Ridge 927 ft and its lowest point at Horine 420 ft. The region operates in the UTC-6.