Van Vleck is a census-designated place in Matagorda County, Texas, United States. The population total represents one of the few areas with positive growth in Matagorda County. The 2010 census showed a 25% increase with 1,844 people. Although near Bay City, the site of Van Vleck falls outside the ETJ of Bay City and is regulated by county police an…Van Vleck is a census-designated place in Matagorda County, Texas, United States. The population total represents one of the few areas with positive growth in Matagorda County. The 2010 census showed a 25% increase with 1,844 people. Although near Bay City, the site of Van Vleck falls outside the ETJ of Bay City and is regulated by county police and county ordinance.