Original building designed by Burnham and Root, 1889-91, 53 West Jackson Boulevard. Designated 
a Chicago Landmark in 1973.  Holabird and Roche built the south addition, 1893, northwest corner of Dearborn and Van Buren Streets.  See construction details and more history of this site at  Chicago Landmarks.

John Root considered the Monadnock Block a challenge to his life's work.  He gave more time to designing it than any other building.  The client was Peter Brooks, who had purchased a lot 100  feet square at a cost of $118,000.   Because of the narrow lot, Brooks knew from the beginning that this would be a tall, narrow building.  Liking Indian names, in the earliest concepts Brooks was already referring to the proposed building as the "Quamquisset."  Later, he renamed it "Mt. Monadnock."

Brooks desired a building almost lacking in ornamentation, and it was thus John Root's challenge to produce it.  Early conceptual drawings indicate a definate Egyptian influence.  The final results met with mixed reviews.  Some could not think of any appropriate adjective except "big," but one writer called the Monadnock Block "a pure expression of business, a building which told its story in the plainest and strongest words, and then stopped talking."

It was recently restored to its original condition, including open elevator cars. 

Appears on this Rand McNally 3-D  map (at the University of Illinois at Chicago):
http://tigger.uic.edu/depts/ahaa/imagebase/intranet/chiviews/page157.html