uc – under care of (Quaker)
UBCJA – United Brotherhood of Carpenters & Joiners of America
UCV – United Confederate Veterans
UDA – United Daughters of America
UDC – United Daughters of the Confederacy
UFT – Ultimate Family Tree (software)
ult. – ultimo (Latin), of the preceding month
unm. – unmarried
upl – using profane language (Quaker)
USIGS – United States Internet Genealogical Society
USGW – USGenWeb (online collective providing genealogical resources via linked webpages)
USV – United States Volunteers (US Civil War)