Chattanooga is the fourth-largest city in the U.S. state of Tennessee, with a population of 167,674 as of the 2010 census. It is the seat of Hamilton County. Located in southeastern Tennessee on Chickamauga Lake and Nickajack Lake, which are both part of the Tennessee River, Chattanooga lies approximately 120 miles (190 km) to the northwest of Atlanta, Georgia, 120 miles (190 km) to the southwest of Knoxville, Tennessee, about 135 miles (217 km) to the southeast of Nashville, Tennessee, about 120 miles (190 km) to the northeast of Huntsville, Alabama, and about 148 miles (238 km) to the northeast of Birmingham, Alabama.