According to the United States Census Bureau, the CDP has a total area of 5.7 square miles (14.8 km²), of which, 5.2 square miles (13.5 km²) of it is land and 0.5 square miles (1.3 km²) of it (8.76%) is water. A navigational channel connects Port Mansfield to the Laguna Madre, to the Intercoastal Waterway (canal), and cutting through South Padre Island, to the Gulf of Mexico. The cut through South Padre Island has shoaled considerably and as of early 2008 only shallow draft boats can safely enter at the Mansfield cut.
There were 187 households out of which 14.4% had children under the age of 18 living with them, 64.7% were married couples living together, 5.3% had a female householder with no husband present, and 26.7% were non-families. 21.4% of all households were made up of individuals and 9.1% had someone living alone who was 65 years of age or older. The average household size was 2.22 and the average family size was 2.50.
In the CDP the population was spread out with 13.5% under the age of 18, 4.6% from 18 to 24, 16.9% from 25 to 44, 37.1% from 45 to 64, and 28.0% who were 65 years of age or older. The median age was 55 years. For every 100 females there were 102.4 males. For every 100 females age 18 and over, there were 107.5 males.
The median income for a household in the CDP was $26,500, and the median income for a family was $27,500. Males had a median income of $18,333 versus $26,667 for females. The per capita income for the CDP was $15,087. About 20.5% of families and 26.8% of the population were below the poverty line, including 53.5% of those under age 18 and 5.4% of those age 65 or over.
In addition, South Texas Independent School District operates magnet schools that serve the community.