Calcium is a census-designated place in Jefferson County, New York, United States. The population was 3,573 as of the 2020 census. The CDP is in the town of Le Ray and includes the hamlets of Calcium and Sanfords Four Corners. Historic landmarks include the stone house at the intersection of State Route 342 and County Route 138 that once served as the post office for the area, and the Calcium Community Church at the same intersection.