Shannon is the name of Ireland's longest river, from the Irish Sionainn, and is usually explained as "old" or "wise river", after the goddess Sionann of Irish legend. It became a girls' name in the United States in the mid-20th century, long before it caught on in Ireland itself. Shannon still ranked number 152 in 2000, but has fallen steadily since and stands at number 2405 in 2025.