I am trying to find the first wife of Eaton E. Hahn, s/o Israel Hahn and Elizabeth Mentzer/Menzer/Meintzer.

This is the Mahoning County, Ohio marriage record for his second marriage:

Hahn, Edin [Eton E.] (26) / Susanna Spaht [Susannah Spait] (26) 1 Mar 1857, C.G. Wm Sigelen, r: 6 Mar [2-211] L: 25 Feb, Israel Hahn. Springfield. [3-230]Eaton (27) b. & r. Springfield Twp, P:Israel Hahn. 2nd marriage. Susannah (30), P: Jacob Spayth. 1st Marriage [5-17]

He was single and living with his parents on the 1850 census so his first marriage was between 18 Sept 1850 and 1 Mar 1857. There must have been at least one child to this marriage because in 1910 he and Susanna are living with his granddaughter, Nora (Hahn) Berkey in Elkhart County, Indiana