I have made a study of the Désilets surname and I have a database. But I don't find your grandfather's marriage in my data. I assume that he married in US. But with a few more details, we should be able to identify him and his line.
- Do you have the name of his parents?
- Do you know his date and place of birth?
- Do you know the name of any siblings and their spouses?
Any other detail may help. Let me know at: firstname.lastname@example.org
The Désilets surname was "invented" in Quebec, twice, so there are two families. It doesn't exist in France. Your ancestor was likely Antoine Desrosiers who arrived in Quebec about 1642.