Isham was born in New York City on July 20, 1853. He was the son of
William Bradley Isham (1827–1909) and Julia (
née Burhans) Isham (1827–1907). His father was a leather merchant who owned downtown factories and warehouses on
Gold and Cliff Streets and became vice president of the
Bank of the Metropolis and the president of the Bond and Mortgage Guarantee Company. Among his siblings were: and brothers,
Samuel Isham, an artist; and William Burhans Isham. In 1862, his father rented the former house and estate of the late Dr. Floyd T. Ferris in uptown Manhattan as a summer residence. The two-story house, located on forty-acres in the neighborhood now known as
Inwood, had been built in the 1850s and was part of the
Dyckman tract. Isham purchased the house and estate two years later in 1864. The Isham children later donated, and sold, parcels of the estate to the City of New York for the creation of
Isham Park. His maternal grandfather was Col. Benjamin Burnhans of
Warrensburg, New York and his paternal grandparents were Charles Isham and Flora (née Bradley) Isham, a daughter of Judge William Bradley of
Hartford, Connecticut. ==Career==