[T]he building was designed by William Dewey Foster and constructed in 1936-37 as part of the W.P.A. (Works Progress Administration) to combat the Great Depression. Foster was responsible for designing structures in both New York City and Washington D.C., including ten post offices in New York City and its immediate suburbs.
Cooper Station was designed in the Classical Revival style and its most dramatic feature is the curve of the facade at the irregular corner of the site. Further highlighting the curve of this building is the two-story colonnade comprised of six receded Doric columns which delineate the corner bays.
The Cooper Station Post Office was listed on the New York State and National Registers of Historic Places in 1982.
Unfortunately, the building is not landmarked.
And other factoid: Newman on "Seinfeld" was said to work at this P.O., and the exterior made a super-quick cameo in "The Package," which originally aired on Oct. 17, 1996...