Santa Monica is a census-designated place in Willacy County, Texas, United States. The population was 86 at the 2020 census. Santa Monica is located at 26°21′56″N 97°35′24″W / 26.36556°N 97.59000°W. According to the United States Census Bureau in 2000, the CDP has a total area of 0.3 square mile, all land. The CDP gained area prior to the 2010 cen…Santa Monica is a census-designated place in Willacy County, Texas, United States. The population was 86 at the 2020 census. Santa Monica is located at 26°21′56″N 97°35′24″W / 26.36556°N 97.59000°W. According to the United States Census Bureau in 2000, the CDP has a total area of 0.3 square mile, all land. The CDP gained area prior to the 2010 census, increasing its total area to 1.0 square mile, all land as before.