St Day is a civil parish and village in Cornwall, England, United Kingdom. It is positioned between the village of Chacewater and the town of Redruth. The electoral ward St Day and Lanner had a population of 4,473 according to the 2011 census.
St Day is in an area that was historically known for mining, encompassing places such as Poldice, Tolcarne, Todpool, Creegbrawse and Crofthandy. The village gained significant wealth from mining activities. It holds a central position within the Cornwall and West Devon Mining Landscape, which is a designated World Heritage Site. This site includes other notable locations such as St Agnes, Chacewater, Chapel Porth and Porthtowan.