Lamar is a small, unincorporated community and census-designated place in Aransas County, Texas, United States, 10 miles north of Rockport and 40 miles north of Corpus Christi. As of the 2010 census it had a population of 636. The community was named for Mirabeau B. Lamar, the second president of the Republic of Texas. This was a new CDP for the 2010 census. Lamar was founded in 1839 at Lookout Point, on the channel entrance to Copano Bay.