Lanark County is a county located in the Canadian province of Ontario. Its county seat is Perth, which was first settled in 1816. Most European settlement of the county began in 1816, when Drummond, Beckwith and Bathurst townships were named and initially surveyed. The first farm north of the Rideau was cleared and settled somewhat earlier, in 1790. The county took its name from the town of Lanark in Scotland.