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.he most prominent natural features in and around Chattanooga are the Tennessee River and the surrounding mountains. The city is nestled between the southwestern Ridge-and-valley Appalachians and the foot of Walden's Ridge; the river separates the ridge from the western side of downtown.