Originally a variant of Helen, although now no longer associated with that name. Initial H- tended to be added and dropped rather capriciously, leading to many doublets (compare for example Esther and Hester). It is also sometimes used as a short form of Eleanor, to which, however, it is unrelated.
Probably an Americanized spelling of German Kötner or Köthner, status names for a cotter, derived from Middle High German, Middle Low German kote ‘shelter’, ‘cottage’, specifically of a kind that was rented on a daily basis and had little or no land with it. See Koth 1.