Coy
Coy is most likely a shortened form of MacCoy/McCoy in Irish usage, though in some cases it may also be a locational surname from a place-name spelled Quoy or Coy.
The #2,597 most common surname in the United States (2010 Census) — about 1 in every 22,252 Americans shares it.
Etymology
The name is not fully settled. One strong line of explanation connects Coy with Irish MacCoy/McCoy, ultimately from Gaelic Mac Bhuidhe, meaning "son of the yellow-haired" or "son of the fair-haired one." In English records, however, Coy can also be a shortened or altered local surname from place-names such as Quoy or Coy, especially in eastern England.
History
The surname appears in both Irish and English-looking contexts, which suggests more than one source. Lower specifically treated Coy as related to McCoy, while Bardsley connected it with a place-name in Cambridgeshire, showing that the same spelling could arise independently. In modern English-speaking countries, Coy is relatively uncommon and may reflect either Irish surname reduction or a local English origin.
Origin
Regions
Variant spellings
Fun fact
The same spelling can point to very different origins: in one tradition it is a shortened Irish patronymic, while in another it is tied to an old English place-name.
From the historical record
“COXON. Coxswain ? COY. ]M'Coy, sans I\Iac. COYFE. See Quaife, which in Kent and Sussex was so spelt until within the last century. COYNE. See Coyney. COYNEY. The manor of Weston- Coyney, in the parish of Caverswall, co. Stafford, seems to have been in possession of the family from temp. Hen. III. B.L.G.”
— Patronymica Britannica: a dictionary of the family names of the United Kingdom