Cheonan is the largest and most densely populated city of Chungcheongnam-do, South Korea, and the third largest city in the Hoseo region after Daejeon and Cheongju. Cheonan borders Gyeonggi-do in the north, Chungcheongbuk-do to the east and southeast, Sejong City to the south and Asan-si and Gongju-si to the west and southwest.