Cass
A surname with more than one possible origin, including an Irish Gaelic personal name and, in some cases, a shortened form of Cassandra.
The #4,679 most common surname in the United States (2010 Census) — about 1 in every 40,726 Americans shares it.
Etymology
Cass can be an Anglicized surname from the Irish Gaelic personal name Cas, an old name meaning roughly "curly" or "twisted" in many Gaelic interpretations, though some 19th-century writers connected it with a verb meaning to turn aside or oppose. In English records, Cass was also treated as a short form of Cassandra, and related surnames such as Case, Casson, and Cash were sometimes explained that way. The surname may therefore have several independent origins depending on the family line.
History
Older heraldic and Irish surname dictionaries both mention Cass, but they do not agree on a single origin. In Irish contexts it appears as an ancient personal name, while in English usage it could arise as a nickname or shortened form of Cassandra. Because the name is brief and phonetically simple, unrelated families may have adopted or inherited it in different regions.
Origin
Regions
Variant spellings
Fun fact
The same short surname could be explained in very different ways by Victorian scholars, which is a good reminder that not all family names have one neat origin story.
From the historical record
“Herald. CASS. Cas, an ancient Irish personal name, found so early as the fifth century. See Macnamara. CASTELYN. See Castelline. CASTELLINE. Castellan, the governor of a castle. CASTERTON. Parishes, &c., in cos. Westmoreland and Rutland.”
— Patronymica Britannica: a dictionary of the family names of the United Kingdom