According to his death record, he died in Boston, was a resident of Brooklyn..
Massachusetts, Deaths, 1841-1915
Name: William H. Deforest
Event Date: 09 Aug 1860
Event Place: Boston, Suffolk, Mass.
Residence: Brooklyn, N.Y.
Marital Status: Married
Birthplace: Woodstock, N.Y.
Estimated Birth Year: 1807