1946 saw the opening of the in Washington D.C. office and the move of the headquarters to yet another location in Chicago.
Since then, the headquarters of ALA have been at 50 E. Huron, Chicago, IL. At the time they were housed in the old Cyrus H. McCormick Mansion.
The building was later torn down, and the current building in the same site was dedicated as ALA headquarters in 1963.
For images of the old Cyrus McCormick Mansion please see the Library History Buff Blog.
The above blog entry also contains information of the proposed building at 50 East Huron from a 1960 postcard.
The ALA Archive has the blueprints and plans for the Cyrus McCormick Mansion.