BAYON LA, a river of the United States, in the state of Louisiana, and one of the numerous arms into which the Mississippi divides itself in the lower part of its course. Near Donaldsonville it separates from the Mississippi in the parish of Ascension, runs through that of Assumption, forms the boundary between the parishes of Terrebonne and Lafourche Intérieure, and, after a S.E. course of nearly 120 miles, falls into the Gulf of Mexico, east of the Bay of Timbalier.