The 'de Erth' family took their name from the lands of Airth which lie close to the barony of Plean in Stirlingshire. This family probably erected the first Plean Castle. The de Erth family ended in an heiress and lands that were acquired by her husband near Tranent near East Lothian were probably named after the heiress's family. The name first appears in about 1235 in East Lothian in a deed by Alanus de Swinton in which a mention is made of the name 'de Elfinstun'. It is likely that de Swinton's son, John, who owned the lands, went on to become John de Elfinstun.

There is a family tradition however, that claims that the family are descended from Flemish knights called Helphenstein. Another theory suggests that the name is derived from Alpin's tun, which means the farmstead of Alpin.

Sir John de Elfinstun married Margaret of Seton who was a niece of Robert the Bruce. One of John's descendants was William Elfinstun who became rector of Kirkmichael. William studied Civil and Canon Law in Paris and he eventually became Professor of Law at that university. He also became Bishop of Aberdeen in 1484 and later Lord High Chancellor of Scotland. William later obtained a bull from Pope Alexander VI in 1494 for founding the University of Aberdeen.

A cousin of bishop William was Sir Alexander Elphinstone who was created Lord Elphinstone by James IV of Scotland. Alexander and the king were together killed at the Battle of Flodden in 1513. Alexander's son, another Alexander Elphinstone, was killed at the Battle of Pinkie Cleugh in 1547.

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