I ran a "metaphone" search on the U.S. Social Security Death Index for "DeGiacomo." Here are the surname variations that came up! You might want to try some of these variations in whatever records or databases you're searching:

De Giacoma
De Giacomano
De Giacomo
Degiacomi
Degiacomo
Dejackimo
Dejackmo
Dejackome
Dejacma
Dejacome
Dejacomo
Dejiacomo
Di Giacoma
Di Giacomano
Di-giacomo
Di Giacomo
Di Jiacomo
Diagiacomo
Digiacamo
Digiacoma
Digiacome
Digiacomi
Digiacomio
Digiacomo
Digicomo
Digiocomo
Dijiacomo