Early usage, you can take the boy out of the country

Solution 1:

Twiddling the Ngram arguments we find a "preprint" of @MarkBannister 's reference, in the May 16, 1914 issue of The Country Gentleman:

Remember the phrase how it's easy to get the boy out of the country but much more difficult to get the country out of the boy.

And there's a fair possibility that this is the first in-print use, as it's quoting Theodore Vail and uses "the phrase" rather than "the old phrase".

Solution 2:

Here's a usage from a yearbook from 1913 (published, it seems in 1913): Second Junior Annual of the Detroit College of Medicine: Recollections and Touches from the Lives of the Various People Connect with the Detroit College of Medicine. There's nothing to indicate that this is a first , or even early, usage though:

JOHN JENNINGS WATTS. Dr. Snyder says you can take the boy out of the country, but you cannot take the country out of the boy. Watts has disproved this. Watts came from the wilds of Ontario, but now he introduces the latest fads into the class, and was the first man in school to wear collars with transverse striations.

Maybe, although I doubt it, Dr Snyder—whoever he actually was— is the originator of this phrase. It's a nice thought.

You can see a pfd of Detroit College of Medicine 1914 Yearbook here. [You need p.126 of the book, if you're interested, which is page 64 of the pdf]

Note

On a webpage from Wayne State University the date of publication is given as 1914. This book was indeed written by the class of 1914. However, as Sven Yargs points out it seem highly probable that it was published in 1913. It anticipates the leaving of the 1913 class. In other words the it was written by the students who would leave the following year. Sven writes in the comments below:

I think that the curator at Wayne State University misread the wording "By the Class of 1914" as meaning "Published in 1914." It doesn't make sense to devote 14 pages of a yearbook to a class that left the year before. From page 102 of the annual (the last page of the Senior section, which includes a lengthy account of the hijinks of the class of 1913): “On May 29th the class of 1913 will meet officially as a class for the last time. Deep in our hearts there is a feeling of regret that we are about to depart.” Clearly, the senior class of 1913 is about to graduate.

This evidence seems to be very strong.