In 2012, the population of Kentucky was an estimate of 4, 380, 415 people and was ranked the 22nd in the U.S. Kentucky has 120 counties in the state. The two largest cities in Kentucky are Louisville and Lexington. There was a route system created in the 1920's. Originally, it was so that odd numbers ran from north to south. The routes KY 101 and higher are larger in sequential orders designated by the Department of Highways.