I. The place
Ayrshire was, from the late mediaeval period, divided into three baronial bailiwicks — Cunninghame in the north, Kyle in the middle, and Carrick in the south. The northern division gave the surname its name. The placename itself is older than its first surviving documentary attestations and has been read by historians of Scots toponymy as a Brythonic compound, sometimes glossed as rabbit-warren or famous district; no single reading has settled the matter, and the safest position is that the meaning is ancient and uncertain.
The earliest documented bearer is generally given as Wernebald, a Flemish-descended tenant who held the lands of Kilmaurs in Cunninghame in the twelfth century under a grant from Hugh de Morville, Constable of Scotland. From Wernebald's family the lordship passed by the usual route — heritable lands, marriage, royal favour — into the lineage that became Clan Cunningham.
II. Clan and Earldom
The chiefly line of Clan Cunningham held the Earldom of Glencairn from 1488, when Alexander Cunningham of Kilmaurs was created the first earl, until the line died out in the late eighteenth century. The fifth Earl, Alexander Cunningham (d. 1574), was a leading figure in the Scottish Reformation and a covenanter; the ninth Earl, William Cunningham (d. 1664), led a Highland-Lowland royalist rising against the Cromwellian regime. Robert Burns wrote his "Lament for James, Earl of Glencairn" on the death of the fourteenth and last earl in 1791, by which point the title was lapsing.
The wider clan was always more a network than a single house. Cunningham as a surname spread early to the cadet branches and to the tenants and servants of the principal lines, and from the fifteenth century onward it appears, in steadily larger numbers, in the ordinary records of the western Lowlands without any necessary link to the Earls' own line.
III. Heraldry
The arms most associated with the surname are those of the Earls of Glencairn: argent, a shakefork sable — a black shakefork, sometimes called a pall reversed, on a silver field. The shakefork is an unusual ordinary in Scottish heraldry and was for a long time treated as the visual signature of the Cunningham family. Cadet branches differenced the arms in the usual ways — by adding a label, a chief, or a charge — but the underlying device persisted.
Family tradition explains the shakefork by reference to a thirteenth-century Cunningham who is said to have hidden the future Malcolm IV of Scotland in a hayloft and covered him with a fork; the explanation is decorative, the arms are documentary.
IV. Variant spellings
The modern double-n form is now overwhelmingly dominant, but is not the oldest. Cunynghame, Cuningham, Cuninghame and Coningham all appear in early records. Conyngham survived as a separately-styled family, granted the Marquessate of Conyngham in the Irish peerage in 1816. In modern Ireland and Scotland the spellings Cunningham, Cunninghame and (rarely) Cuningham all coexist, with the simple double-n form by some distance the most common.
V. Spread to Ireland
The decisive transmission of Cunningham from Scotland to Ireland was the seventeenth-century Plantation of Ulster, in which thousands of Scots tenants were settled across Antrim, Down, Donegal, Tyrone, Armagh and Fermanagh on lands forfeited from the Gaelic Irish lordships. Cunningham was a frequent surname in the Ayrshire and Galloway flow and arrived in Ulster in the same proportion. From there it spread south and west by ordinary internal migration through the eighteenth and nineteenth centuries.
By the time of Griffith's Valuation (mid-nineteenth century) the name was settled in every Irish county in modest numbers, with the heaviest concentrations in Donegal, Down, Antrim, Galway, Roscommon and Mayo. It is, by some distance, one of the more common surnames in Ireland of plainly Scottish origin.
VI. The wider diaspora
The same waves that took most Scots and Ulster-Scots names overseas took Cunningham: emigration to North America from the early eighteenth century onward, to the British colonies of Australia and New Zealand from the early nineteenth, and a steady professional and commercial movement to the imperial centres of the East. Today the name is well represented in Canada, the United States, Australia and New Zealand, with smaller settlements in South Africa, India, and the West Indies.
Several cities, towns, mountains and watercourses outside Scotland take the name from a settler family or a Royal Navy admiral: Cunningham, Kentucky; Cunningham, Kansas; Mount Cunningham in British Columbia; the Cunningham highway in Queensland.
VII. See also
A list of well-documented bearers of the surname, across periods and fields, is at Notable Cunninghams. The companion entry on the forename Jennifer is at Jennifer. A note on why the combined name is so common is at The combined name.