On 17 October 1889, he married Caroline Ames Ladd (3 September 1861, Portland OR - 12 June 1946, Glen Cove), the daughter of William S. Ladd and Caroline Elliott.
They had three children:
Charles Pratt (1892- ), President of the Board of Pratt Institute from 1937-1953
Mary Caroline Pratt (1895-1980), who married attorney Christian Herter.
He later served as Governor of Massachusetts (1953-1956), and Secretary of State (1959-1961).

Helen Ladd Pratt (1899-1972), who married a Mr. Emmett.

Pratt commissioned Charles A. Platt to design the family county estate, known as "Poplar Hill", in Glen Cove, on the North Shore of Long Island.
Since 1971 it has been owned and operated by Glengariff Healthcare Center.

Pratt commissioned a family home at 229 Clinton Avenue, Brooklyn, designed by noted New York architect Henry F. Kilburn.
It was originally known as the "Frederic B. Pratt House" (it is now known as the Caroline Ladd Pratt House).
It was completed in 1898 in a neo-Georgian style.
The family donated the property to the Pratt Institute.

Pratt died May 3, 1945 at his family home in Glen Cove, aged 81, of a heart ailment.
He was survived by his wife, who died a year later, and grown children.
On 17 October 1889, he married Caroline Ames Ladd (3 September 1861, Portland OR - 12 June 1946, Glen Cove), the daughter of William S. Ladd and Caroline Elliott. They had three children:
Charles Pratt (1892- ), President of the Board of Pratt Institute from 1937-1953
Mary Caroline Pratt (1895-1980), who married attorney Christian Herter. He later served as Governor of Massachusetts (1953-1956), and Secretary of State (1959-1961).
Helen Ladd Pratt (1899-1972), who married a Mr. Emmett.
Pratt commissioned Charles A. Platt to design the family county estate, known as "Poplar Hill", in Glen Cove, on the North Shore of Long Island. Since 1971 it has been owned and operated by Glengariff Healthcare Center.
Pratt commissioned a family home at 229 Clinton Avenue, Brooklyn, designed by noted New York architect Henry F. Kilburn. It was originally known as the "Frederic B. Pratt House" (it is now known as the Caroline Ladd Pratt House). It was completed in 1898 in a neo-Georgian style. The family donated the property to the Pratt Institute.
Pratt died May 3, 1945 at his family home in Glen Cove, aged 81, of a heart ailment. He was survived by his wife, who died a year later, and grown children.
Frederic B. Pratt