According to the U.S. Census Bureau, the county has a total area of 511 square miles (1,320 km), of which 464 square miles (1,200 km) is land and 47 square miles (120 km) (9.2%) is water.
As of the census of 2000, there were 28,658 people, 11,822 households, and 8,842 families residing in the county. The population density was 62 people per square mile (24/km²). There were 16,241 housing units at an average density of 35 per square mile (14/km²). The racial makeup of the county was 97.64% White, 0.07% Black or African American, 0.61% Native American, 0.18% Asian, 0.03% Pacific Islander, 0.25% from other races, and 1.20% from two or more races. Approximately 1.04% of the population were Hispanic or Latino of any race. Among the major first ancestries reported in Stone County were 24.3% American, 20.4% German, 11.3% English, and 10.8% Irish ancestry.
There were 11,822 households out of which 25.60% had children under the age of 18 living with them, 64.70% were married couples living together, 7.20% had a female householder with no husband present, and 25.20% were non-families. 21.40% of all households were made up of individuals and 10.30% had someone living alone who was 65 years of age or older. The average household size was 2.40 and the average family size was 2.76.
In the county, the population was spread out with 21.40% under the age of 18, 6.20% from 18 to 24, 23.80% from 25 to 44, 29.70% from 45 to 64, and 18.90% who were 65 years of age or older. The median age was 44 years. For every 100 females, there were 96.20 males. For every 100 females age 18 and over, there were 93.10 males.
The median income for a household in the county was $40,487, and the median income for a family was $46,675. Males had a median income of $26,224 versus $19,190 for females. The per capita income for the county was $21,813. About 8.50% of families and 12.80% of the population were below the poverty line, including 19.00% of those under age 18 and 8.10% of those age 65 or over.