Duffy ranks #845 with 139 male registrations. The name is an Irish surname ("descendant of Dubthach," meaning "dark one") and on a pet license usually carries the same warm Irish-diminutive register as Murphy or Sully: heritage worn lightly.
The Irish-surname diminutive cluster
Duffy sits with Murphy, Sully, Finn, and Brody in the cluster of Irish surnames that work better as pet names than as human names in current American use. The naming logic is consistent: families with Irish heritage or affection for the sound pick the surname for the dog while reserving longer or more formal first names for human use.
Sound and breed lean
Two syllables, front-stressed (DUF-fee), with a hard D opening and a soft -y close. The shape calls warmly outdoors and pairs naturally with the affectionate household register. Duffy also pulls a smaller cultural cluster from singer Duffy (the Welsh soul singer of "Mercy") which lends a slight indie-music register for some younger owners. The name lands across breed types but appears notably on Irish setters, wheaten terriers, and shaggy mixed-breed dogs whose temperament owners read as friendly.
The counter-reading
The honest read is that Duffy is a comfort-zone Irish pick. Households who want the Irish register with more distinctive flavor might consider Finn or Murphy. The human Duffy page shows minimal SSA presence; this is comfortably pet territory.