St Just, known as St Just in Penwith, is a town and civil parish in the Penwith district of Cornwall, England, United Kingdom. It lies along the B3306 road which connects St Ives to the A30 road. The parish encompasses the town of St Just and the nearby settlements of Trewellard, Pendeen and Kelynack: it is bounded by the parishes of Morvah to the north-east, Sancreed and Madron to the east, St Buryan and Sennen to the south and by the sea in the west. The parish consists of 7,622 acres of land, 12 acres of water and 117 acres of foreshore. The town of St Just is the most westerly town in mainland Britain and is situated approximately 8 miles west of Penzance along the A3071. St Just parish, which includes Pendeen and the surrounding area, has a population of 4,637. An electoral ward of the same name also exists: the population of this ward at the same census was 4,812.
St Just lies within the Cornwall Area of Outstanding Natural Beauty. St Just is one of only two towns included within the Cornwall AONB.