The original collection includes letters received, 1877-1931, letter books, 1888-1909, personal memorandum books, and other records. The papers for the years up to 1887 relate to minor local matters in Pierce County during his terms in the legislature and to very routine matters, chiefly railroad passes, during his service as railroad commissioner. For the years of congressional service the collection consists largely of correspondence with constituents, chiefly in regard to patronage and pension claims, but also touches upon the subject of Republican Scandinavian politics and newspapers, local affairs in Pierce County, a proposed bridge at Superior and other local Superior affairs, the tariff, temperance issue, Bennett law, state campaigns including his own campaign for the state gubernatorial nomination in 1894 and that of Robert M. LaFollette in 1896, efforts of stockholders of Beef Slough Boom Company to obtain government assistance, and the River Falls Light, Heat and Power Company of which Haugen was president and the introduction of natural gas for illumination, heating, and power purposes. Running through the years up to 1900 is the subject of Wisconsin politics, including about a dozen letters in the 1890s of LaFollette and a few of Samuel A. Harper. The bulk of the papers for 1895-1900 relate to Haugen's law practice at River Falls.

For the years of Haugen's work as tax commissioner, the papers are largely personal, although there is a little material on the subject of the income tax law of 1911, and in 1919-1920 there is correspondence with officials of the National Tax Association of which Haugen was then president, relating to association activities, studies, conference programs, and policies, and tax legislation and problems.

After Haugen left the commission, he served off and on for the next two years as adviser to the Board of Equalization of Montana on revision of state tax laws, and especially railroad, public utility, bank, and inheritance tax legislation. There is correspondence with Montana tax officials, including several letters of Governor Joseph M. Dixon, and considerable material on Montana state politics for the five or six years following 1921.

In the 1920s, there is also information on contemporary Wisconsin politics and reminiscent correspondence on Wisconsin politics of the previous third century. His autobiography, based on these papers, has been published in the Wisconsin Magazine of History.