According to the U.S. Census Bureau, the county has a total area of, of which is land and is water. In total area, Kenedy is the 13th largest county in Texas. In land area only, it is the 25th-largest county in Texas. It borders the Gulf of Mexico. Baffin Bay makes up much of the border with Kleberg County.
As of the census in 2000, there were 414 people, 138 households, and 110 families residing in the county. The population density was 0.28 people per square mile. There were 281 housing units at an average density of 0.19 per square mile. The racial makeup of the county was 64.49% White, 0.72% Black or African American, 0.72% Native American, 0.48% Asian, 31.88% from other races, and 1.69% from two or more races. 78.99% of the population were Hispanic or Latino of any race. There were 138 households, out of which 35.50% had children under the age of 18 living with them, 58.70% were married couplesliving together, 10.90% had a female householder with no husband present, and 19.60% were non-families. 18.80% of all households were made up of individuals and 6.50% had someone living alone who was 65 years of age or older. The average household size was 2.97 and the average family size was 3.26. In the county, the population had widespread age groups including 29.20% under the age of 18, 9.70% from 18 to 24, 26.30% from 25 to 44, 24.20% from 45 to 64, and 10.60% who were 65 years of age or older. The median agewas 34 years old. For every 100 females, there were 110.20 males. For every 100 females age 18 and over, there were 100.70 males. The median income for a household in the county was $25,000, and the median income for a family was $26,719. Males had a median income of $18,125 versus $12,188 for females. The per capita income for the county was $17,959. 15.30% of the population and 9.90% of families were below the poverty line. Out of the total people living in poverty, 15.60% are under the age of 18 and 18.80% are 65 or older. Kenedy County, the third least populous county in Texas, had 108 times more cattle than people in 1999.
Like the rest of South Texas, Kenedy County regularly supports candidates from the Democratic Party. Its county seat, Sarita, is ranked as the most liberal city in Texas. The Republican Party has carried the county only six times since the 1928 presidential election. Despite its Democratic-leaning, the county has become competitive in recent years due to the Hispanic voters becoming more open to voting Republican, and no presidential candidate since Bill Clinton in 1996 has carried the county by more than a 20 vote margin. In statewide races for governor and the U.S. Senate, the county has slowly trended Republican. The last Democrat to carry the county in a gubernatorial race was Tony Sanchez in 2002, while Rick Noriega in 2008 is the last Democrat to carry it in a senatorial race.
