There were a number of "John's towns" in Scotland but the earliest record of the surname is a John Johnstone at the end of the 12th century Later, Sir John Johnston of Dumfries signed the Ragman Roll in 1296, along with most of the other Scottish landowners, swearing allegiance to King Edward I. The family grew in stature and Sir John's descendants were appointed as a warden of the western marches in 1381. Adam Johnstone was named Laird of Johnstone near the beginning of the 15th century and took part in the Battle of Sark in 1448. Adam's son assisted King James II in his struggle with the Douglas family and was rewarded with land near Threave Castle which had previously belonged to the Douglases. Adam's eldest son (another John) was the ancestor of the Annandale branch of the family while another son Mathew is said to have married a daughter of the Earl of Angus (chief of the Red Douglases) and his descendants formed the Westerhall branch.

The Johnstones were one of the many Border families who frequently raided the north of England over the centuries. They also became involved in one of the many Border feuds with the Maxwells, which was only resolved by the intervention of King James VI in 1623.

James Johnstone, the chief of the clan, was made Lord Johnstone of Lochwood in 1633 by King Charles I and Earl of Hartfell in 1643. King Charles II elevated him to Earl of Annandale, and Lord Johnstone of Lochwood, Lochmaben, Moffatdale and Evandal. In 1701, a descendant was raised to the rank of Marquess of Annandale.

In early times, the city of Perth was called St John's Toun (the local football team is still called St Johnstone) and when surnames became more frequent, many of the people from there took the name Johnstone. When the MacGregor name was proscribed (banned) a number of that clan took the name Johnstone.

Other Johnstones are to be found in Strathspey, unconnected with those in the Borders. This family supported the Jacobite cause in 1715 and 1745. The head of this branch now lives in America.

In more modern times, Tom Johnston, a Labour politician, was a successful Secretary of State for Scotland during the Second World War.

The Johnston clan motto is "Nunquam non paratus" which means "Never unprepared".

Johnston/Johnstone combined was the 10th most frequent surname at the General Register Office in 1995.

http://www.rampantscotland.com/clans