1590s, "ignorant, dull," from Boeotia, district around Thebes in ancient Greece (said to have been so called for its cattle pastures; Greek bous = "ox"), whose inhabitants were characterized as proverbially dull and countrified by their neighbors, the Athenians. The Boeotians presumably held reciprocal opinions, but their great writers, Plutarch and Pindar, though patriots, are full of praise for Athenian deeds and institutions.
Though his aim was to vindicate Boeotia, [Pindar] has probably done her a disservice, in that he has helped to immortalise the scurrilous proverb Βοιωτία ύς, which he wished to confute. ... If left to itself, the slander might have passed into oblivion long ago. [W. Rhys Roberts, "The Ancient Boeotians," 1895]