The collection is arranged into the following 28 series:
Series I. Abraham Overholt & Company, 1881-1888
Series II. Carnegie Brothers & Company, Ltd., 1867-1894
Series III. Carnegie Company, 1900-1901
Series IV. Carnegie Steel Company, Ltd., 1892-1900
Series V. Carnegie, Phipps, & Company, Ltd., 1887 to 1893
Series VI. Cerro de Pasco Companies, 1901-1925
Series VII. Clairton Brick & Manufacturing Company, 1901-1904
Series VIII. Clairton Street Railway Company, 1905-1916
Series IX. Correspondence, 1883-1919
Series X. Ephemeral Material, 1878-1947
Series XI. Faraday Coal & Coke Company, 1862-1934
Series XII. Frick Building, 1897-1983
Series XIII. Henry Clay Frick Coke Companies, 1871-1900
Series XIV. Highland Building, 1909-1922
Series XV. Hump Removal, 1899-1914
Series XVI. Jellico Coal Lands, 1903-1943
Series XVII. Josiah Vankirk Thompson, 1914-1920
Series XVIII. Shaw Coal Company, 1890-1925
Series XIX. St. Clair Improvements Company, 1901-1915
Series XX. St. Paul Coal Company, 1914-1926
Series XXI. Union Arcade Building/Union Trust Building, 1906-1948
Series XXII. Union Trust Company, 1895-1921
Series XXIII. Union, Joliet, and Illinois Steel Companies, 1884-1902
Series XXIV. United States Steel Corporation, 1899-1919
Series XXV. Westmoreland- Fayette Historical Society, 1906-1987
Series XXVI. William Penn Hotel, 1890-1925
Series XXVII. Pittsburgh Atlases and Plat Maps
Series XXVIII. Maps and Architectural Drawings