The "kin" portion is of Dutch or Danish origin (-kijn), which then gained a certain popularity in England.
[3] The first use of the name "Jenkins" or "Jenkens" in England occurred as early as 1086 as a diminutive of the English form of John.
[6] At that time, it was a direct reference to the name John in the formal and diminutive forms and not associated with birth order.
Its earliest documented occurrence was in Monmouthshire, in the Domesday Book of 1086, but it almost certainly predates the Norman Conquest.
[7] A common English use, leading to use as a surname, may have been the now-obsolete "little Johns", a 12th-century term for the Cornish (and later Welsh) people, either alluding to their comparatively small stature or, more likely, classing them as illegitimate offspring of the unpopular King John of England, who was previously the Earl of Cornwall and Gloucester.