I have three Mannix brothers who emigrated to the US in the early 1860s, William, Luke & Patrick sons of James and Margaret Mannix. William seemed to have been in Tennessee (working on the railways)and then New Orleans prior to posting a notice in the Boston Pilot Missing Persons (try Google search) seeking info on his two brothers Luke and Patrick. William was born c.1824 , Luke 1826 and Patrick around 1838 all in Pollardstown, Co Cork, Ireland. William later settled in Bexar Co Texas married to Alice Henry and Luke appears to have settled in Ottumwa, Wapello Co Iowa.
Their parents and siblings emigrated to Australia.
If you think there's a connection would be glad to hear from you.