Hannibal is a city along the Mississippi River in Marion and Ralls counties in the U.S. state of Missouri. According to the 2010 U.S. Census, the population was 17,916, making it the largest city in Marion County. The bulk of the city is in Marion County, with a tiny sliver in the south extending into Ralls County.
Developed for river traffic, today the city is tied to vehicle traffic, intersected by Interstate 72 and U.S. Routes 24, 36, and 61. It is across the river from East Hannibal, Illinois. Hannibal is approximately 100 miles northwest of St. Louis, 210 miles east-northeast of Kansas City and 194 miles miles east of Saint Joseph, and approximately 100 miles west of Springfield, Illinois.
Hannibal is not the county seat, but it has one of two county courthouses. There is also one in Palmyra, the county seat, which is located more centrally in the county. Hannibal is the principal city of the Hannibal, Missouri micropolitan area, which consists of both Marion and Ralls counties.