There are various ways of spelling Mehigan/Mehegan and it is pronounced in Ireland as Meegan. Castle Mehigan townland in 1901/1911 has no Mehigan's living on it. The farthest back records I have are the 1828 Tithe Applotment records for Charles Mehigan and the Widow Mehigan of Castle Mehigan townland, Charles and Cornelius of Canavee townland, Timothy of Cairnbeg, John of Carriggeengour (Carrikeen Gour), James of Doogh (Dough), Denis of Clohanailleen, Patrick of Tourmore (Toormore), Daniel of Oughtmina/minee and John of Ship. (was he on a ship?)
In 1901/1911 the oldest living Mehigan was Charles of Cannawee (note the various spellings of same townland), age 70 and his wife Ellen who was a Sheehan whose brothers went to Montgomery Minnesota as did their son John. Also James of Dunlough whose wife was Kate Leary and whose daughter Anne went to Buffalo NY in 1895. So this conceivably leaves alot of Mehigan's that left between 1828 and 1901.
Let me know if this info is helpful to you or anyone else reading this post. Thanks! Mary Jean