One of the earliest settlements on Bayou Lafourche was called Valenzuela. Spain established a military post and Spanish officials promised to provide farming equipment, land and a church in the center of the post. This proviso was carried out at several of the new settlements, but not at Valenzuela. The nearest church was Ascension, but it was too distant and too difficult to reach. Spain granted land in 1793, and the first little church was built and placed under the invocation of the Assumption of the Blessed Virgin Mary. Father Bernardo de Deva, a Spanish Capuchin, served as first pastor. When the United States took over the Louisiana colony, most of the Spanish missionary friars returned to Spain. Father De Deva, however, stayed, became a secular priest and continued to serve the Lafourche section. In 1818, a cornerstone was laid for a new and better church. In 1838, a diocesan seminary was established nearby. It was staffed by the Vincentian Fathers who also served the parish. The seminary burned in 1855, but the Vincentian priests continued in the parish until 1858 when floodwaters washed away all traces of the church and seminary.
In 1825, an American congregation, the Sisters of Loretto at the Foot of the Cross, opened a school in Plattenville. Their knowledge of French was limited, and they had difficulty working with the parishioners. They turned the school over to the Sacred Heart Sisters from Convent, Louisiana in 1828. In 1833, they passed control of the school to the Sisters of Mount Carmel who established their first house in Louisiana in Plattenville. They left in 1838 when the school building was needed for the new seminary.
The present Assumption Church, dedicated in 1856, was built of bricks made of clay in Plattenville. In 1984, Assumption Parish was clustered with Immaculate Conception and St. Anne Parishes. The people of the church of the Assumption remain full of good will, enthusiasm and love for their church, willing to sacrifice to preserve the ancient and venerable church at Plattenville. Though the physical appearance of the parish of Assumption of Blessed Virgin Mary has changed with the passing of time, the faith and devotion of its people is still evident today, as it must have been in the past, to guide its people all these years.