'Cary' often represents an old Somerset and Devonshire surname; whereas 'Carey' is usually an Irish surname with at least seven distinct Gaelic-Irish derivations (see Carey page), and also a Norman-French surname, a variant of 'de Carrey'.
However, both forms are synonymous: the 1871 Census shows Carey as the more common form, even in Somerset and Devon.
1) The surname Cary is today most frequently found in Somerset, probably named from Castle Cary in that county. It occurs early, e.g. in the Somerset 'Feet of Fines': Philip de Kary (1203), Gunilda de Kary (1235), Peter de Cary (1280). There were several Bristol merchants of the name in the 16th/17th centuries, who (confusingly) adopted the roses arms of the Devon Carys, with the addition of a golden anchor (v. Burke, 'Gen. Armory). The surname was found in both forms in Somerset in the 1871 Census: Cary 110; Carey 220.
2) The landowning Cary family of Devon (Cockington and Clovelly) may be named from the place in Devon recorded as 'Kari' (Pre-Celtic or Celtic language) in the Domesday Book (1086), an estate on the river Cary or Carey in West Devon. The root meaning is uncertain: Old European 'kar'- 'hard, stony' according to Watts (Cambridge, 2003) or Celtic 'car'- 'friendly, pleasant' (Eckwall, Oxford, 1963). This family's eponymous ancestor appears in the 1564 'Visitation of Devon' as 'John Cary of Cary'.
Sanson de Cari held lands in 'Buckland' in Devon in 1197 (Devon Feet of Fines, No. 4). In the 1871 Census we find: Cary 14; Carey 54.
3) Cary is also indigenous to France, and is found mainly in the Nord region; the derivation may be from Old European 'kar'- 'stone, stony place' (J-P Dickes, Boulogne, 1986). Carey also is indigenous to France: mainly Normandy, Burgundy (in all France, 1,674 bearers - according to nom-famille.com). These names, plus Carrey, Carry, are probably cognate.
4) Cary/Carey is also a Cornish surname, and probably derives from the same Old European root 'kar'- 'stone/stony', as in Carey Tor on Bodmin Moor. There is some confusion with Carew in this county, from local names Kerrow etc., from Cornish 'ker/car',meaning 'fort/encampment'. 1871 Census figures are: Cary 26; Carey 10.
The Devon Cary arms in the 'Visitation' were: 'argent, on a bend sable, three roses of the field; crest: a swan proper' (v. also Burke, 'General Armory', 1884; and Images, below). Their motto was 'virtute excerptae'. Anciently this family is alleged to have borne different arms: 'gules, a chevron between three swans, argent' (v. Burke, op. cit.) .
The best known branch of the Devon Carys, were the Barons Hunsdon (created 1559), who from the 16th century spelt their name 'Carey'. William Car(e)y of Chilton Foliat, Wiltshire was a member of Henry VIII's court; he was a cousin of Henry VIII through his Beaufort grandmother. Carey married Mary Boleyn, Queen Anne Boleyn's sister, in 1520; his children, then, were doubly cousins to Queen Elizabeth. Charles 1 awarded them the titles 'Earls of Monmouth' (1626) and 'Earls of Dover' (1628): similar arms as those of Devon Cary, (see Images below). They became extinct in 1765.
Another branch of the Devon Cary family were made Viscounts Falkland in the Scottish peerage (1620) by Charles 1; this title was upgraded to the Earldom of Falkland (1722) in the Jacobite peerage of the exiled Stuart king, James. Their name is spelt 'Cary', and they are the sole surviving branch.
Sir George Car(e)y of Cockington was Lord Deputy/Treasurer of Ireland 1598-1606; he described Catholic clergy there as a 'wicked rabble', although his father and brother were both Catholic. His relation, Sir Henry Cary, 1st Viscount Falkland, was Charles 1st's Lord Deputy of Ireland 1622-28; he tried, unsuccessfully, to banish priests in 1623; again, his own wife and son were Catholics. (Refs: historyofparliamentonline.org). The Carys of Cockington, latterly of Torre Abbey in Torquay, became extinct in the male line in 1916, with the death at the Somme of Lieut. Launcelot Robert Sulyarde Plantagenet Cary.
In fact, the Devon Carys were known as 'papists' and 'recusants' throughout the period. 'Papist' Sir Edward Cary of Cockington, had his estates sequestrated on the 20 May 1646. The Carys of Long Melford, Suffolk (orig. Devon) were also Catholics; a son, Edward, was made chaplain to James 11's army. The Catholic 6th Baron Hunsdon, Robert Carey, was made Colonel of the 12th Foot in 1688, in the army of James 11, whom he served in Ireland at the Battle of the Boyne, and whom he followed into exile.
The last of the Clovelly Carys, the Anglo-Irish Carys of Redcastle/Whitecastle, Inishowen, Donegal (from whom sprang the author Joyce Cary) petered out in the 20th century; their arms were the same as Cary of Devon, with the motto 'sine macula'. (The numerous Careys of the Glens of Antrim are native Irish and unconnected).
A Cromwellian Captain, Peter Cary, a Devon man, obtained land on the Blackwater in N.E. Cork in the 17th century; he and his wife are recorded in the '1659 Census'. The property became known as 'Careysville'. The family later bought Glenabbey, now known as 'Carey's Castle', just south of Clonmel, Tipperary in the 18th century. By then their name was 'Carey'; never a large family they became extinct in the last century. It is their arms, similar to Devon Cary, which appear under 'Carey' in Kennedy's 'Book of Arms' (1816). Needless to add, they had no connection to the very numerous native Carey families found in both Cork and Tipperary, and elsewhere in Munster.
The Welsh-Norman family named from Carew in Pembrokeshire may be the source of some bearers of Cary/Carey in Wales, with the proviso that many Careys there would be of Irish immigrant stock. Welsh Carews are also recorded as settled in the West Country in the late Middle Ages (see Carew page). However, Carew in Cornwall may be indigenous, from Cornish locative names Kerrow, Caroe, &c. the derivation being similar to that in Wales.
Carey as such is the name of a Channel Island family long established in St Martin's Parish, Guernsey, whose name is a variant of the Norman French Carrey. Families of the Carrey/Carey are recorded in Eure, Seine-Maritime and Calvados. The Guernsey Careys have no known connection to the West Country Carys, although confusingly from the 1580s they used the same arms, which they registered in 1915, with a crescent added.
In Griffith's 'Valuation' (1846-64) of Ireland Carey households were far more numerous than Cary, with 1, 308 households to 33.
The 1891 Census of England showed roughly twice the number of Carey in Lancashire (746) than in Somerset (347); this reflects the growing number of Irish immigrants to G.B. in this period.
In modern Britain, telephone directories show highest numbers of 'Carey' located in areas of Irish immigration: Greater London, Greater Manchester & Lancashire, West Yorkshire, West Midlands and the Glasgow area.