Newellton is a town in northern Tensas Parish in the northeastern part of the U.S. state of Louisiana. The population was 886 in the 2020 census, a decline of 596 persons, or 40 percent, from the 2000 tabulation of 1,482. Newellton is west of the Mississippi River on Lake St. Joseph, an ox-bow lake. Further south toward St. Joseph, the parish seat of government, is another ox-bow lake, Lake Bruin, a part of which is the popular Lake Bruin State Park.