St. Helena, originally part of Mary Jemison's Gardeau Reservation, was settled after she sold most of her property in 1823 and grew into a prosperous riverside hamlet with a flour mill, two sawmills, a shingle mill, paper mill, two general stores, a hotel, and 25 dwellings. In the 1880s, 75 pupils attended its school from September through December, and the schoolhouse also served as a church and community center. Three bridges at St. Helena were destroyed by floods or ice; the first, built in 1835, was a covered structure with wooden latticework sides. By the 1930s, few people still lived there, and utility companies acquired the land for a planned power-generating dam at Mt. Morris. In 1950, as a flood-control dam neared completion, the last homes were removed, the cemetery was relocated to Castile, and the bridge was dismantled. Today the fields and foundations of St. Helena lie under 15 feet of mud left by flood waters held behind the Mt. Morris Dam, and only the bridge's end abutments remain on either side of the river.