As Helmut already pointed out, Eichenau was almost certainly a hamlet now located in the community of Kirchberg an der Jagst. In the 1870s it was part of Oberamt (equivalent to county) Gerabronn in Württemberg. For church purposes Eichenau belonged to the parish of Lendsiedel, whose parish books are available at ancestry.com (and presumably ancestry.au) and at archion.de.
I have located the baptismal record of Georg Köhn (born 28 March 1871, baptised 1 April) here: https://www.ancestry.com/sharing/21051339?h=3765a1&utm_campaign=bandido-webparts&utm_source=post-share-modal&utm_medium=copy-url. For those who have access to archion.de but not ancestry.com, the record is located at http://www.archion.de/p/8e666abe92/.
The quality of the digitisation is not the best, but what I can make out is: Georg, son of Jakob Köhn, innkeeper (Gastwirth) and farmer, and his wife Marie Rosina, nee Richendörfer (or Buchendörfer?), born at Eichenau Tuesday, 28 March, 5:30 p.m., baptised at Eichenau Saturday, 1 April, by the minister, godparents (1) Georg Wesel [??], bachelor from Kirchberg, (2) Heinrich Kurz, wagonmaker from ??, (3) Christian Krause, pastrymaker (Conditor) from Kirchberg.