As of the census of 2005 estimate, there were 137,004 people, 38,792 households, and 30,102 families residing in the county. The population density was 224 people per square mile (87/km²). There were 40,795 housing units at an average density of 85 per square mile (33/km²). The racial makeup of the county was 85.78% White, 11.40% Black or African American, 0.28% Native American, 0.62% Asian, 0.04% Pacific Islander, 1.13% from other races, and 0.76% from two or more races. 2.35% of the population were Hispanic or Latino of any race.
There were 38,792 households out of which 39.40% had children under the age of 18 living with them, 61.70% were married couples living together, 11.60% had a female householder with no husband present, and 22.40% were non-families. 18.10% of all households were made up of individuals and 5.60% had someone living alone who was 65 years of age or older. The average household size was 2.75 and the average family size was 3.11.
In the county the population was spread out with 28.20% under the age of 18, 8.20% from 18 to 24, 32.70% from 25 to 44, 22.10% from 45 to 64, and 8.90% who were 65 years of age or older. The median age was 34 years. For every 100 females there were 98.00 males. For every 100 females age 18 and over, there were 95.00 males.
The median income for a household in the county was $48,206, and the median income for a family was $53,590. Males had a median income of $38,032 versus $26,474 for females. The per capita income for the county was $20,468. 7.10% of the population and 5.60% of families were below the poverty line. 8.30% are under the age of 18 and 9.50% are 65 or older.
DeSoto County has the second highest per capita income in the State of Mississippi.