The St. Lawrence Iroquoian language is an extinct language that was once spoken by the Iroquoian people living in the St. Lawrence River Valley in North America. It is part of the larger Iroquoian language family, which includes languages like Mohawk and Seneca. This language was primarily used until the 17th century, when European colonization led to significant changes in the region. The decline of the St. Lawrence Iroquoians and their language was influenced by factors such as disease, warfare, and cultural assimilation. Today, it is studied by linguists and historians to understand the culture and history of the Iroquoian peoples.