Calcium is a hamlet (and census-designated place) in Jefferson County, New York, United States. The population was 3,516 as of July 2007.
Calcium is in the Town of Le Ray and was formerly called Sanford's Corner.
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. The church was built in 1853 by a group of at least three different denominations, including Methodist Episcopal, Christian, and Unitarian. The building was shared by these and various Christian groups over the years, and remains a community church today.