1907-1930. Papers from this period deal mainly with Petersen's civic role in Askov, the business of his American Publishing Company, and his early career in Minnesota state politics, up to his election to the State House of Representatives in 1930. Petersen carried on a good deal of correspondence on behalf of the village of Askov, aimed mainly at improving utilities and developing organizations within the area. There are also letters from individuals seeking Petersen's assistance with personal and business problems. Some letters to and from political figures in the state solicit his support in the columns of the Askov American. Petersen's unsuccessful campaigns for the office of state representative in 1926 and 1928 mark the beginning of the extensive political campaign correspondence between Petersen and the voters, as well as with Farmer-Labor Association officials. There is a notable exchange of letters with Henry G. Teigan, as well as some correspondence with Farmer-Labor Association headquarters regarding support articles in the Askov American.

1930-1936. The correspondence from the years of Petersen's service in the state legislature consists mostly of supplications from job seekers and his letters of recommendation for state jobs for friends and constituents. There are also letters and other papers dealing with taxes and taxation, especially the state income tax law, which Petersen was instrumental in passing. Also included is correspondence regarding the election of Charles Munn as speaker of the state house of representatives (November and December 1932). The 1934 correspondence mainly concerns the successful Olson-Petersen gubernatorial campaign. Beginning in 1935, but culminating in 1936, is much correspondence with friends and fellow politicians reflecting Petersen's dissatisfaction with Olson's leadership, which he felt relied too heavily on the advice of a handful of insiders, the "Mexican Generals." A copy of a letter which Petersen wrote to Olson, voicing his criticism, is included (August 12, 1936). Much of his unhappiness stemmed from the handling of political appointments, since he felt that favoritism and patronage were filling the state bureaucracy with political cronies who could be counted on to campaign in any election for the person who appointed them. Petersen therefore began to call for improved civil service legislation. The correspondence for the first half of 1936 is also filled with speculation about Olson's health and the effect his death might have on the elections that fall. There is also a good deal of materials related to Petersen's attempt to wrest the Farmer-Labor Party nomination for governor from the hands of Olson's "Crown Prince," Elmer Benson. Very little correspondence is present pertaining to Petersen's four-and-a-half month term as governor, commencing with Olson's death in August. However, some material related to the National Governors' Conference, which Petersen attended (filed November 16-18), and copies of speeches he gave during that time are present, as well as a copy of his message to the special session of the legislature (December 17) and his farewell message to the legislature (January 5, 1937). The majority of Petersen's gubernatorial papers are in the Minnesota State Archives.

1937-1946. In the general election of 1936 Petersen was elected to a six-year term as Railroad and Warehouse Commissioner, while Benson became governor. Petersen's papers continue to deal mainly with politics, although there is some information about the activities of the Railroad and Warehouse Commission. Specifically, there is some discussion about whether responsibility for the regulation of public utilities should rest with state or local government, an inquiry into telephone rate increases in the Twin Cities area and Duluth (1937-1940), an investigation of the expenses of former Commissioner A. C. Laurisch and of the Commission's Oil Inspection Department by the Joint Legislative Investigating Committee in 1939, and a review of streetcar fares in St. Paul. A copy of the latter's "report, findings of fact and order" is filed November 6, 1941, along with a copy of Petersen's dissent from the majority opinion. A similar report on streetcar rates in Minneapolis is filed April 8, 1943. Petersen's gubernatorial campaigns of 1938, 1940, and 1942 are fully documented, including pieces of campaign literature. Files for the 1942 campaign are the most complete. Alleged corruption in state government, accusations of Communism, and counter-charges of anti-semitism figured prominently as campaign issues. During this time Petersen emerged as the leader of the right wing of the Farmer-Labor Party, and Benson as the leader of the left wing. Taxes, old age pensions, U. S. involvement in World War II, and the unpopular Lien Law (passed in 1939) were discussed in these campaigns. Of particular interest is opposition to the Lien Law from members of the Chippewa nation in 1942. At the end of 1937 there is some mention of the Independent Workers Alliance of Minnesota, and in 1938 and 1939 there is correspondence with the Independent Progressive Voters of Minnesota. The possibility of a merger between the Democratic and Farmer-Labor parties is discussed as early as 1939 (see a letter of March 7) and again in 1940 (December 30 and 31) and 1941 (January 18).

Petersen spoke out strongly against any involvement in World War II and received mail from America First committees, including a letter from Robert E. Wood, chairman of the national committee, announcing the committee's dissolution after the bombing of Pearl Harbor (December 16, 1941). Petersen also favored an aggressive third-party movement on a national scale, as evinced by his correspondence of 1935-1938. His support of the controversial Father Coughlin also drew constituent comment in 1936. Non-political subjects covered in the correspondence of these years include the visit of the Crown Prince and Princess of Denmark to Minnesota in the spring of 1939, and the celebration of the Askov American's twenty-fifth anniversary that September. From 1943 through July of 1945 there is a lull in the political correspondence, as Petersen gave up an active role in public life due to poor health. During this time he worked briefly for the Federal Cartridge Corporation of Minneapolis and for the Office of Defense Transport, where he served as principal transportation liaison officer of the Transport Personnel Division. This job took him temporarily to San Francisco in the spring of 1945, and his letters to his family and friends in Minnesota describe much of his work. He also wrote about the charter convention of the United Nations, which was taking place in San Francisco. The collection contains some printed material pertaining to the convention. The 1946 campaign files contain much information relating to Petersen's unsuccessful bid for the Republican Party nomination for governor. The taxable value of iron ore mined in Minnesota and shipped across the Great Lakes and the conservation of the state's natural resources were major campaign issues, as well as the old age pension and Lien Law and conditions at the Minnesota School for the Feeble-Minded at Faribault.

1947-1954. The third section of the papers is much less extensive. There is practically nothing from 1947 to 1950. From 1951 to 1954 the correspondence mainly concerns Medora Petersen's activities with the local and state Parent-Teacher associations and the National Congress of Parents and Teachers, and her teaching career in Morris, Minnesota. The PTA material mainly describes workshops, conventions, and meetings, but also includes a series of publicity bulletins (1956-1958) originating with the National Congress Committee on Publicity. There are also copies of documents pertaining to the teaching of home economics, such as a paper called "Strengthening the Family Relationship Aspects of Home Economic Teaching at the Secondary Level," prepared under the auspices of the American Home Economics Association (1953), and a series of leaflets on teaching home economics (budgeting, home management, shopping) used at a conference of home economics teachers at the University of Minnesota (1958). Starting in 1957 some anti-war, anti-draft, anti-bomb material appears, mostly originating with the American Friends Service Committee or the Women's International League for Peace and Freedom. There is a series of Washington Newsletters from the Friends Committee on National Legislation in 1957 and 1958, and newsletters from the Congress of Racial Equality (CORE) in 1958. Petersen was elected Railroad and Warehouse Commissioner again in 1954 and 1960 but there is little campaign material from those years. For both terms there is some information about the commission's business: urban mass transit (including consideration of bus fares in the Twin Cities), regulation of public utilities, grain inspection and livestock weighing, a complaint against excessive charges for long-distance phone calls (filed September 19, 1956), and the transportation of liquid gas (1965).

1955-1968. The political papers begin again in 1955 when Petersen agreed to manage the primary campaign of Senator Estes Kefauver. Kefauver won the Minnesota primary, but withdrew before the nominating convention in August. Petersen attended the convention as a Kefauver delegate; a copy of the "Temporary Role of Delegates and Alternates to the Democratic National Convention" is included (August 13, 1956). In 1958 Petersen challenged Eugene J. McCarthy for the Democratic nomination to the United States Senate, and there are some campaign materials from that drive.

The newspaper clippings document Petersen's political life. They are arranged chronologically by year, and by month when appropriate. Clippings from the 1938 and 1940 campaigns are the most complete.

Mounted press clippings, which often overlap with those in the newspaper clippings series.