The Unionville Borough Building is located off State Route 504; Borough mailing address: PO Box 81, Fleming PA 16835.
The borough of Unionville is a station upon the Bald Eagle Valley railroad with post office designation of "Fleming." The site of the borough was purchased in 1843 by Zephaniah Underwood, who in connection with his son William laid it out in town lots in 1848. John Peters subsequently laid out an addition to it. It was incorporated as a borough by a decree of the Court December 3, 1859, and the Bald Eagle Valley railroad was completed through it as early as 1864. Fleming post-office laid out and it retains that designation.