DeKalb Junction is a hamlet and census-designated place located in the town of DeKalb in St. Lawrence County, New York, United States. Its population was 519 as of the 2010 census. DeKalb Junction has a post office with ZIP code 13630. U.S. Route 11 passes through the community.According to the U.S. Census Bureau, the community has an area of 3.945 square miles; 3.883 square miles of its area is land, and 0.062 square miles is water.