Our Casefile Clues sale (20% off) is still going on through the end of today (there’s still time if you missed it). If you ordered and have not heard from me, please email me at mjnrootdig@gmail.com. More information is here.
Not all immigrants to the United States naturalized, especially before the early twentieth century. It is possible your ancestor never bothered to naturalize. If your ancestor had no interest in voting, he may have never seen a need to naturalize as that’s a key element of citizenship. In some locations and in some time periods, aliens (generally non-naturalized immigrants) were not able to own land. State statute would indicate when that changed. During the time period when only citizens could own land, that was for many a key reason to naturalize.
We’ve had unexpected response to our offer, so we are running it again this weekend. From now through 11:59 p.m. 3 August 2015, a subscription to 52 issues of Casefile Clues is only $17. Your subscription can be processed here. Easy to understand, well-written, and genealogically sound, see records discussed and “next steps” planned out. We have updated our list of back issue topics here. 
Have you tried to locate voter’s registration lists for your ancestor? Typically kept at the local level (usually the county) they can provide detailed information on your ancestor. Some may provide citizenship details, residential information, and age. At the very least they would imply that the relative was eligible to vote.
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