First of all, there is no such document as "Declaration of Naturalization." One may find a Declaration of Intent, a Petition for Naturalization or a Certificate of Naturalization.
Locating any of these documents depends on the date of the naturalization and the court of record. I assume that Frankfort is the county of residence of the subject at the time of the naturalization. While there is a high correlation between county of residence and filing of naturalization documents prior to 1922, it is no guarantee. After 1922 there is a better method.