The National Register of Historic Places, to which the Monadnock was added in 1970, noted that "the sheer, unadorned walls of this building forming a powerful mass became, prophetically, a forerunner of the 'slab skyscraper'—a style not popular until the late 1920s" and that "the two sections ... make, as an ensemble, one of the strongest, yet refined architectural statements in the development of twentieth century architecture." Its nomination as a National Historic Landmark in 1976, as part of the South Dearborn Street – Printing House Row Historic District, included the comment that it was "one of the most classical statements ever made in the skyscraper idiom."