In 1862, Isham rented as a summer residence a house and property in uptown Monhattan, in the neighborhood now known as Inwood, from the estate of Dr. Floyd T. Ferris, a well-known physician who had died seven years earlier.
It's notable that when Isham was having a wall built or reconstructed along the Broadway edge of the estate, a workman found an old milestone which read "12 Miles from New York", which had once stood on the Kingsbridge Road (which became Broadway).