The earliest instance of this error that I found is in the Rand McNally Bible Atlas (Emil G. Kraeling, 1956).  That same year the Westminster Historical Atlas to the Bible (Wright and Filson) published it correctly as Farah.  The error was immediately followed by the influential Denis Baly, The Geography of the Bible (1957). Other sources have it named correctly, including The Land of the Bible (Aharoni), Baker Bible Atlas (Pfeiffer), Atlas of the Bible (Grollenberg), and New Atlas of the Bible (Negenman).  Some newer volumes have it correct as well, including the New Bible Atlas (Bimson) and The Oxford Guide to People and Places of the Bible (Metzger and Coogan).