Catherine Barrett , Galway Jan.28,1869

I have a marriage certificate from County Galway, dated January 28, 1869.
It is for the marriage of my grt.grt.grandfather , Simon Larkin, age 25 to Catherine Barrett age 17. Catherine Barretts' father is listed as Michael Barrett, Simon Larkins' is listed as Simon Larkin.The marriage certificate is from the registrars distict of Ballinasloe.The witnesses were Patrick Larkin and Bridget Barrett.
I don't know what relation they were to the happy couple.
Are any of these names familiar ? I would love to hear from anyone who can fill in some blank spots, such as how their daughter Mary (May) ended up in Brooklyn.
Thank you in advance.