Coosa is part of the Alexander City micropolitan area.
From 2000 to 2003, Coosa County's growth rate of -5.8% made it the biggest percentage population loser among the state's 67 counties. Annette Jones Watters of the University of Alabama's Alabama State Data Center cited Coosa as one of eight counties to lose greater than 6% of its population from 2000 to early 2007.
As of the census of 2000, there were 12,202 people, 4,682 households, and 3,408 families residing in the county. The population density was 19 people per square mile (7/km²). There were 6,142 housing units at an average density of 9 per square mile (4/km²). The racial makeup of the county was 63.94% White, 34.19% Black or African American, 0.32% Native American, 0.04% Asian, 0.01% Pacific Islander, 0.62% from other races, and 0.88% from two or more races. 1.29% of the population were Hispanic or Latino of any race.
There were 4,682 households out of which 30.00% had children under the age of 18 living with them, 54.80% were married couples living together, 13.50% had a female householder with no husband present, and 27.20% were non-families. 24.30% of all households were made up of individuals and 9.80% had someone living alone who was 65 years of age or older. The average household size was 2.52 and the average family size was 2.98.
In the county the population was spread out with 23.70% under the age of 18, 8.60% from 18 to 24, 29.00% from 25 to 44, 24.30% from 45 to 64, and 14.40% who were 65 years of age or older. The median age was 38 years. For every 100 females there were 104.40 males. For every 100 females age 18 and over, there were 102.50 males.
The median income for a household in the county was $29,873, and the median income for a family was $36,082. Males had a median income of $25,390 versus $18,171 for females. The per capita income for the county was $14,875. About 11.80% of families and 14.90% of the population were below the poverty line, including 19.50% of those under age 18 and 13.40% of those age 65 or over.