There was a mail stage route into and through Ionia prior to 1909. As such being rather long running, the route would be known by the locals as well as the post office even after discontinuance. Therefore my belief/guess is that as the former "stage route" and road ways used were known, it was still a good name for the addressee's mail.
From:
http://genealogytrails.com/mich/ion...oniatwp.html --
Quote:
Ionia Post-Office
The post-office in Ionia was established in 1835, and Erastus Yeomans appointed to the charge thereof. He kept the mail in his log house, at the western end of the village; but, that location being publicly inconvenient, he removed pretty soon to the centre of the town and occupied a building erected expressly for post-office purposes. Ionia was at first on a mail-route between Jackson and Grand Rapids, and received mail once in two weeks by the hands of a horseback-rider. When the stage route was opened between Detroit and Grand Rapids via Ionia, mail came in daily.
Mr. Yeomans was succeeded in 1841 by Jacob Winsor, who kept the office in the tailor's shop of Ethan S. Johnson. Mr. Johnson was Winsor's deputy; and when popular objection to the latter compelled his resignation Johnson got the appointment, in 1842. Richard Dye succeeded Johnson in 1845, and thereafter the incumbents were Jonathan Tibbitts, from 1849-57; William Yerrington, 1857-61; Lewis D. Smith, 1861-69; Edward Stevenson, 1869-73; M. L. Smith, 1873-77; Alfred M. Heath, 1877 to the present.
The business of the Ionia office for the three months ending June 30, 1880, is shown in the following: Received for sales of stamps, stamped envelopes, box-rent, etc., $2,100.87; received for domestic money-orders issued, $7,668.24 ; received for foreign money-orders issued, $208.30; paid on domestic orders, $5,565.45; paid on foreign orders, $82.79; fees on money-orders, $88.90.
Edited for missing "n" on a word.
2nd Edit: One source still listed "Stage Route" as the address location for a family as of 1917.