Decker is a town in Johnson Township, Knox County, Indiana, United States. The population was 249 at the 2010 census. It was founded 1869 by Isaac Decker. Decker is near the White River, and is well known for the watermelon and cantaloupe produced in the surrounding rural area.The school at Decker provided all grades until 1967, when the middle and high school grades were consolidated into South Knox High School.