The Irish surname Moylan is an Anglicization of the Gaelic "O'Maoileain", which is well known in Munster in the forms Mullane and Mullins. It is most likely derived from the word "maol", which literally means "bald"; the surname thus means "son/descendant of the bald man." The name was originally applied to a man noted for this feature, and was subsequently used to refer to his offspring.

Today the name Moylan is particularly associated with Co. Cork; several notable bearers of the name have hailed from that county. Brigadier General Stephen Moylan was considered by Washington to be among his ablest officers; his brother Francis was Bishop of Cork from 1786 to 1815. Sean Moylan (1888-1957) was a prominent member of the Irish independence movement and was the Minister for Agriculture at the time of his death.

Early references of the name date back to the sixteenth century, when a "pardon" is recorded as having been granted to one Donaghe O'Moylan of Derryknackane, Co. Limerick in 1586. It is also numerous in the Hearth Money Rolls for Co. Tipperary (1666).