It is the hometown of Mark Twain and the setting of his The Adventures of Tom Sawyer. Historical sites related to Mark Twain and sites depicted in his fiction have become an important part of the towns legacy.
Hanibal was also the birthplace of singer and actor Cliff Edwards ("Ukelele Ike").
According to the United States Census Bureau, the city has a total area of 39.1 km² (15.1 mi²). 37.8 km² (14.6 mi²) of it is land and 1.2 km² (0.5 mi²) of it is water. The total area is 3.12% water.
There are 7,017 households out of which 32.5% have children under the age of 18 living with them, 48.0% are married couples living together, 13.6% have a female householder with no husband present, and 35.1% are non-families. 30.6% of all households are made up of individuals and 15.0% have someone living alone who is 65 years of age or older. The average household size is 2.40 and the average family size is 2.98.
In the city the population is spread out with 25.8% under the age of 18, 10.5% from 18 to 24, 26.3% from 25 to 44, 20.6% from 45 to 64, and 16.8% who are 65 years of age or older. The median age is 36 years. For every 100 females there are 86.7 males. For every 100 females age 18 and over, there are 81.8 males.
The median income for a household in the city is $29,892, and the median income for a family is $37,264. Males have a median income of $30,677 versus $20,828 for females. The per capita income for the city is $16,902. 14.1% of the population and 11.3% of families are below the poverty line. Out of the total people living in poverty, 18.2% are under the age of 18 and 10.8% are 65 or older.