Lake Sumner is a census-designated place (CDP) in De Baca County, New Mexico, United States. The population was 86 at the 2000 census. According to the United States Census Bureau, the CDP has a total area of 68.3 square miles (177 km2), of which, 62.2 square miles (161 km2) of it is land and 6.1 square miles (16 km2) of it (8.94%) is water.
As of the census of 2000, there were 86 people, 44 households, and 27 families residing in the CDP. The population density was 1.4 people per square mile (0.5/km²). There were 188 housing units at an average density of 3.0/sq mi (1.2/km²). The racial makeup of the CDP was 90.70% White, 1.16% Asian, 3.49% from other races, and 4.65% from two or more races. Hispanic or Latino of any race were 17.44% of the population.