Julian Hill Whittlesey (October 27, 1905 – May 20, 1995 ) was a prominent American architect and planner who co-founded the firms Mayer & Whittlesey and then Whittlesey Conklin + Rossant.
Whittlesey was born in Greenwich, Connecticut. He studied civil engineering and architecture at Yale (degrees in 1927 and 1930). He also studied on a fellowship to the American School of Classical Studies in Athens.
In the early 1930s, Whittlesey worked for the Resettlement Administration and the U.S. Public Housing Administration. During World War II, he designed military-related housing and administrative buildings.
In 1935, he co-founded Mayer & Whittlesey, with Albert Mayer. The firm designed Manhattan House and other large buildings. They also helped design the cities of Kitimat, British Columbia, and Chandigarh, India. In the 1950s, he co-founded Whittlesey, Conklin & Rossant, based in Reston, Virginia.