Clarksville is located adjacent to the Mississippi River and is on US Route 79 about nine miles southeast of Louisiana. Clarksville Island is in the Mississippi east of the Missouri-Illinois state line. According to the United States Census Bureau, the city has a total area of, of which is land and is water.
As of the census of 2010, there were 442 people, 210 households, and 109 families residing in the city. The population density was. There were 271 housing units at an average density of. The racial makeup of the city was 89.4% White, 7.2% African American, 2.0% from other races, and 1.4% from two or more races. Hispanic or Latino of any race were 2.9% of the population. There were 210 households, of which 23.8% had children under the age of 18 living with them, 36.7% were married couples living together, 8.6% had a female householder with no husband present, 6.7% had a male householder with no wife present, and 48.1% were non-families. 40.0% of all households were made up of individuals, and 18.5% had someone living alone who was 65 years of age or older. The average household size was 2.10 and the average family size was 2.83. The median age in the city was 45.8 years. 21.5% of residents were under the age of 18; 9.8% were between the ages of 18 and 24; 17.7% were from 25 to 44; 30% were from 45 to 64; and 21% were 65 years of age or older. The gender makeup of the city was 51.8% male and 48.2% female.
2000 census
As of the census of 2000, there were 490 people, 225 households, and 134 families residing in the city. The population density was 1,060.2 people per square mile. There were 278 housing units at an average density of 601.5 per square mile. The racial makeup of the city was 88.57% White, 7.14% African American, 0.20% Asian, 0.20% Pacific Islander, 1.43% from other races, and 2.45% from two or more races. Hispanic or Latino of any race were 3.06% of the population. There were 225 households, out of which 28.0% had children under the age of 18 living with them, 41.3% were married couples living together, 13.8% had a female householder with no husband present, and 40.4% were non-families. 35.6% of all households were made up of individuals, and 15.6% had someone living alone who was 65 years of age or older. The average household size was 2.18 and the average family size was 2.78. In the city the population was spread out, with 25.3% under the age of 18, 8.0% from 18 to 24, 28.0% from 25 to 44, 20.4% from 45 to 64, and 18.4% who were 65 years of age or older. The median age was 36 years. For every 100 females, there were 86.3 males. For every 100 females age 18 and over, there were 83.9 males. The median income for a household in the city was $23,611, and the median income for a family was $29,375. Males had a median income of $29,375 versus $17,292 for females. The per capita income for the city was $14,728. About 22.3% of families and 22.2% of the population were below the poverty line, including 32.2% of those under age 18 and 11.4% of those age 65 or over.
