This collection consists of personal and business papers of A.B. Cook. The papers are divided into several major groupings: A.B. Cook's personal papers, his ranching records, his business records, his political records, and family papers.

The bulk of the correspondence (1888-1928) is in A.B. Cook's personal subgroup. This correspondence includes intermixed, personal, ranch, construction, and other business matters. Among the most substantive correspondence is that with his personal secretary Hazel Alsterberg, who conducted much of his business dealings. She reported to him regularly on the conduct of business. In addition to the correspondence, this subgroup includes court papers (1895-1929); financial records (1886-1928); legal documents (1886-1928) concerning Helena property holdings, mining claims, etc.; reports and subject files (1887-1928) concerning mining properties and other investments; and miscellany. There is a small subgroup of A.B. Cook Estate materials (1928-1932).

The A.B. Cook Stock Farms subgroup includes court papers (1890, 1921); employment records (1915-1954) including payrolls, time sheets, employment applications, and monthly labor reports; financial records (1913-1928), including inventories of the various ranches; legal documents (1882-1928) documenting the ranch properties; organizational records (1919) including articles of incorporation, bylaws and minutes; production records (1901-1933) consisting primarily of extensive Hereford cattle registration and breeding records; subject files (1912-1928) on a wide variety of topics; and miscellany.

The Flying U Ranch subgroup includes a small amount of general correspondence (1907-1911); employment records (1908-1909); financial records (1906-1912); and legal documents (1892-1912).

The Stiles Cattle Company subgroup consists of interoffice and general correspondence (1917-1928) concerning the operation of a ranch on the Standing Rock Indian Reservation; financial records (1918-1926); production records (1918-1923); and miscellany (1922-1924) including maps and lists of lands leased and purchased on the Standing Rock Reservation.

Records of A.B. Cook's Bynum Reservoir Contract consist of correspondence and court papers (1912-1914) of a lawsuit by the Teton Cooperative Reservoir Company; financial records (1908-1912); and legal documents (1909).

Records of Cook and Woldson, Railroad Contractors include correspondence, employment records, financial records, and legal documents (1895-1900) documenting work for the Gaylord and Ruby Valley Railway, the Montana Railroad, the railroad spur to the Parrot Smelter at Whitehall, and other jobs; and railroad specification and bid papers.

The Cook Construction Company subgroup consists of general and interoffice correspondence (1912-1925) of the offices of the company in St. Paul, Minnesota; Montreal, Quebec; and Halifax, Nova Scotia; court papers (1906-1907, 1914) including the seizure of company property by Canadian Customs, for alleged misquoting of value of equipment; financial records (1913-1921); an agreement (1916) with Wheaton Brothers for work on the Halifax Ocean Terminals Railway; copies of organizational records (1912-1921) re the founding and dissolution of the company; subject files (1911-1924) concerning various jobs contracted by the company including work in Sudbury, Ontario; Bulwer Junction, Minnesota; Halifax, Nova Scotia, and Montreal aqueduct and power development projects.

The Cook Tunnel Company / New Gould Mining Company subgroup includes general correspondence (1921-1928); and other materials concerning A.B. Cook's extension of the mining tunnel at Gould, Montana.

Records of McConnell, Cook, and Company and its successor A.B. Cook's Missoula real estate business consist of correspondence (1889-1928); financial records (1889-1928) including a lot ledger, financial statements, tax assessments, etc.; legal documents (1889-1929) including partnership agreements, deeds, certificates of redemption for delinquent taxes, etc.

The Montana Independent Telephone Company subgroup consists of general correspondence (1908-1915), prospecti, and subject files (1909-1913) concerning the merging of several small independent telephone companies into a statewide network.

There are minor business subgroups for the Banner Mining Company, the Buckeye Mining and Milling Company, the Gloria Mining Company, the Lexington Mining Company, the Montana Concrete Construction Company, the National Life Insurance Company of Montana, Shannon and Cook, the Silver Bow National Bank, the Toronto Construction Company, the Trail Creek Coal Company, and the Tuttle Land Company.

Documentation of A.B. Cook's activities in the "Republican Party include correspondence and financial records concerning the 1889 and 1892 elections; a petition for a post office for Tin Cup; petitions for Frank O. Lowden for President, and miscellaneous campaign materials.

The Frank Hervey Cook subgroup includes correspondence (1908-1949); financial records (1921-1955) consisting mostly of bank statements and cancelled checks for Cook, for the C.R. Cattle and Sheep Company, and the Cook Candy Company; several reports; and school records.

The Lena Gosnell Bowyer Finley Cook subgroup consists of incoming correspondence (1929-1933) from family and friends; financial statements (1929-1930); estate materials (1934); and European travel itineraries and brochures.

There are very small subgroups for Margaret A. Cook, for Mary Morgan Cook, for Gloria Cook, and for Mary Agnes Cook.