Henry Janeway Hardenbergh (February 6, 1847 - March 18, 1918) was a U.S. architect, best known for having designed The Dakota luxury-apartment building and the Plaza Hotel, both near Central Park in Manhattan.

Hardenbergh was born in New Brunswick, New Jersey and apprenticed from 1865 to 1870 in an architecture firm in New York. In 1871, het set up his own practice. He obtained his first contracts—for Rutgers College in New Brunswick—through family connections: his grandfather, Jacob Rutsen Hardenbergh, had been the first president of Rutgers College from 1785 to 1790, when it was still called "Queen's College".

His career took off when he got the contract to design the Vancorlear apartment building on West 55th Street in New York in 1879. The following year he was commissioned by Edward S. Clark, then head of the Singer Sewing Machine Company, to build a housing development (1880 - 1886). As part of this work, he designed the Dakota building. Subsequently, he received commissions to build the Waldorf (1893) and the Astoria (1897) hotels for the Astor Estate in New York; both were demolished in 1929 so that the Empire State Building could be erected.

He built several other buildings in similar styles, including the Plaza Hotel in New York (1905 -1907), or the Copley Plaza (1912) on Copley Square in Boston, Massachusetts.

Hardenbergh lived for some time in Bernardsville, New Jersey and died 1918 in New York City.