Ia of Cornwall was a 5th or 6th-century evangelist and martyr who lived in the region of St Ives. According to tradition, she was an Irish princess and the sister of Erc of Slane. After being left behind by her companions during their journey to Cornwall, she is said to have crossed the Irish Sea on a floating leaf. Upon her arrival, she joined Gwinear and Felec to spread the faith in the area.