Lachlan is as Scottish as haggis and tartan plaid kilts, a favorite used throughout England, Scotland, Australia and New Zealand, and just beginning to be noticed in the US -- it reached the Top 1000 for the first time in 2013. An ancient name, Lachlan was originally used to describe the Viking invaders of Scotland, those from the land of the lochs.
In Ireland, the name was Anglicized as Laughlin; in Scotland the pet forms are Lach, Lachie or Lockie.
Lachlan has been a top name in Australia for at least a decade and is currently Number 3 there. It has been in the headlines recently via the eldest son of media mogul Rupert Murdoch.
Somewhat surprisingly, Lachlan has US presidential cred, as the son of tenth president John Tyler, whose other children included a Lyon, a Letitia, a Tazewell and a Pearl.