St. Martinville is a city in, and the parish seat of, St. Martin Parish, Louisiana, United States. It lies on Bayou Teche, sixteen miles south of Breaux Bridge, eighteen miles southeast of Lafayette, and nine miles north of New Iberia. The population was 6,114 at the 2010 census, down from 6,989 in 2000. It is part of the Lafayette Metropolitan Statistical Area.
St. Martinville is located at 30°7′30″N 91°49′50″W (30.125053, -91.830593).
According to the United States Census Bureau, the city has a total area of 3.0 square miles (7.8 km²), of which 3.0 square miles (7.8 km²) is land and 0.33% is water. Its terrain is mixture of swamp and prairie.
In the 16th century, the area between the Atchafalaya River, in Louisiana, the Gulf of Mexico and Trinity River, in Texas, was occupied by numerous tribes or subdivisions of the Attakapan people.