The European country that first colonized the Gulf Coastal Plains was Spain.

The Gulf Coastal Plains were initially settled by Spain in the 16th century, during the Age of Exploration, making it the first European nation to do so. Pánfilo de Narváez and Hernando de Soto were two Spanish explorers who entered the area and claimed large areas for the Spanish Crown. To promote Christianity and ease trade, missions and towns were established. The Gulf Coast's cultural and architectural legacy is influenced by Spain, which shaped regional customs and behaviors. This early colony had a major influence on the history and development of the area by laying the foundation for later European interests and contacts.