June 26 1938 was the date set for the cornerstone of the new post office on South Main and West Lincoln Avenue. It was placed on the southeast corner facing Main Street. Inside the cornerstone are the following items; membership rolls of the Ada churches and rural area churches served by the Ada post office; rolls of the Ada public schools and Ohio Northern University; names of members of all regularly organized fraternal groups, clubs, , both social and service, granges, also boy and girl scout organizations; members of the grand lodge of Ohio; members of the post office staff; engineers and architects of the building; Ada officials, including members of the fire department; a small silk American flag; copy of Bible and prayor book; copies of local publications including the Ada Herald, Northern Review, Ohio Northern general catalogue, year book and high school paper; and a coin of 1938 mintage.