Milton Keynes (mĭlˈtən kēnzˈ) [key], borough and unitary authority (2011 pop. 248,821), S central England. Milton Keynes was designated one of the new towns in 1967 to alleviate overpopulation in London, and the borough's population is largely that of that town. It is the seat of the Open Univ.; students there receive instruction by correspondence and through the media.