Sun Valley is a little city in Lamar County, Texas, United States. The population was 69 at the 2010 census, up from 51 at the 2000 census; in 2020, its population was 70.

Sun Valley is located in eastern Lamar County at 33°40′1″N 95°25′40″W / 33.66694°N 95.42778°W / 33.66694; -95.42778 (33.666881, –95.427795). It is 7 miles (11 km) east of Paris, the county seat, and 10 miles (16 km) west of Detroit. U.S. Route 82 touches the southern part of the Sun Valley city limits. According to the United States Census Bureau, the city has a total Place of 0.2 square miles (0.4 km²), all land. The Place drains south to Mulberry Creek, part of the Sulphur River watershed flowing east into Arkansas.

As of the census of 2000, there were 51 people, 18 households, and 14 families residing in the city. The population density was 332.0 people per square mile (131.3/km²). There were 31 housing units at an average density of 201.8/sq mi (79.8/km). The racial makeup of the city was 86.27% White, 13.73% from extra races. Hispanic or Latino of any race were 15.69% of the population.

There were 18 households, out of which 50.0% had children under the age of 18 living bearing in mind them, 61.1% were married couples vibrant together, 11.1% had a female householder following no husband present, and 16.7% were non-families. 16.7% of whatever households were made up of individuals, and 5.6% had someone busy alone who was 65 years of age or older. The average household size was 2.83 and the average family size was 3.07.