The townland is probably Sheeaun, and recorded with a variation in spelling. Sheeaun townland is in Clonkeen civil parish, and was part of Loughrea Superintendent Registrar's District, and Athenry sub-district, so fits with that birth.
see the entry on the Placename database for the townland. (note there are several different townlands in Co. Galway with the same name)