Maiden Stone and Wexflyer, thanks for your replies. I'm trying to eliminate (or confirm) this Terence Keating as the one baptised 5 March 1838 in Dublin, the son of Jeffrey Keating and Sarah Duffy.
The marriage info for Terence King and Mary McGurk on 3 Dec 1876 came from a copy of the original return of the births, marriages, and deaths filed by the municipality of the city of Elizabeth NJ that occurred in that municipality during the preceding year. His parents are given as Terence and Mary, but I wondered if this was accurate, given that these are the same names of himself and his wife, also the mistranscription of his surname as King not Keating. The return is compiled from the marriages that took place during that year - individual marriage certificate were not issued until June 1878.- so there's room for error there. There's no mention of religious affiliation.
The only census entry I've found which might be him is in 1870 Elizabeth NJ:
Tem (Terr?) Katon, 30, moulder, born Ireland, parents both born Ireland
Kate Katon, 25, KH (keeping house), born Ireland, both parents born Ireland.
Unfortunately it doesn't give the relationship of Kate and Terence. She could be a wife who died before his marriage to Sarah McGurk in 1876, or maybe a sister or other relation.
Terence Keating died in December 1879 and was buried in Mt Olivet Cemetery on 10 December. He appears in the Mortality Schedule for the year ending 31 May 1880, age 40, born Ireland, parents born Ireland.
I haven't found a record of his emigration. I did find a record of his Civil War service in relation to his dependents. His service is recorded as CF, 8 N J Inf and F 6 U S Vet Vol Inf. He is recorded as Terence Cadden - this surname was used by his two daughters.