Gilliam
A surname ultimately derived from William, often appearing in forms influenced by Gill- or Guillaume.
The #1,204 most common surname in the United States (2010 Census) — about 1 in every 10,497 Americans shares it.
Etymology
The historical sources link Gilliam to William, treating it as a variant or reduced form of that very common given name. Some 19th-century writers also connect it with French Guillaume, the continental form of William, which helps explain spellings such as Guilliam. In short, the surname developed as a patronymic from the personal name William rather than from a place or occupation.
History
The name is found in medieval English records and later appears in several spelling variants, including Gillam, Gillham, Guilliam, and Gilliatt. Older surname dictionaries often grouped it with a wide family of William-derived surnames such as Tillson, Gillott, and Gilliatt. In modern English-speaking countries, Gilliam is best known in the United States, though the surname has older British roots.
Origin
Regions
Variant spellings
Fun fact
One 19th-century reference explicitly glossed a Mr. Gilliam as meaning “Guillaume,” reinforcing the surname’s William connection.
From the historical record
“GILLETT. See Gillet. GILLIAM. See William. GILLIATT. See William. GILLIE, A menial servant. Jaraicson. GILLIES. Gael. Gille Jesa, the Ser- vant or Follower of Jesus ; " a youth under the protection of Jesus." .Johnstoue'.s Anecd. of Olave the Black. 1780. GILLING. Two wapentakes and a”
— Patronymica Britannica: a dictionary of the family names of the United Kingdom