winthrop married mary tallmadge trevor in 1892. they had two daughters, emily and katherine. in new york city, they resided in a townhouse in murray hill, manhattan, until they moved to 15 east 81st street on the upper east side. they summered at groton place, a 150-acre estate spreading across the baldhead mountain in lenox, massachusetts whose main house was designed by carrère and hastings and whose grounds included 500 peacocks and pheasants. his wife predeceased him in 1900. his daughters were educated by private tutors; despite his attentive parenting, they both eloped with the help: one with a chauffeur, the other one with an electrician.