Postmark New York to Louisville, Ky., this cover sporting a #26 Type III (I believe).

Addressed to Mrs. S. M. Thustin care of L. T. Thuston Esq.
L.T. (Luther Thayer, 1817-1889) was a bigshot in Louisville in the mid to late 1800s. Found him referred to as Col. and Judge. He was also Secretary of the Mutual Life Insurance Company of Kentucky from its founding in 1866.
Mrs. S. M. possibly his wife or sister-in-law?
Had obviously been displayed in someone's photo album for many years, as shown by the photo corner 'shadow's'.