Chattanooga is the fourth-largest city in the U.S. state of Tennessee, with a population of 167,674 as of the 2010 census, and an estimated population of 171,279 in 2012. It is the seat of Hamilton County. Located in southeastern Tennessee in East Tennessee, on Chickamauga Lake and Nickajack Lake, which are both part of the Tennessee River, Chattanooga lies approximately to the northwest of Atlanta, Georgia, to the southwest of Knoxville, Tennessee, about to the southeast of Nashville, Tennessee, about to the northeast of Huntsville, Alabama, and about to the northeast of Birmingham, Alabama. Chattanooga abuts the Georgia border and is where three major interstate highways meet: I-24, I-75, and I-59.