The papers of Jerome J. Day were in no discernible order when received; therefore a series order was imposed during processing.

The first series contains correspondence and two miscellaneous items. At least two alphabetical groups and two loose-leaf note books were found during the initial processing of this group, therefore there are three subseries for the correspondence. The first spans the years 1905 to 1941 and appears to be remnants of several filing systems, probably merged by Henry in an incomplete attempt to create a subject arrangement; these folders were placed in alphabetical order during processing. It contains personal as well as some business correspondence. There are letters from his wife, daughter, and son, with a few of Jerome's letters to them included. There is also correspondence with the head of the Moran School for Boys which Jerome Jr. was attending when he drowned which detail local efforts in the search for the boy's body. Letters to his brothers and sisters comment on family matters and the business of the mining companies. Other letters concern his political life and a wide variety of business interests, including mining properties, mining stocks, the Northport and Pennsylvania smelters, the Tamarack and Custer mine, and other investments.

The second subseries was already in alphabetical order. It spans the years 1928-1933 and is similar to the previous subseries in content.

The third subseries was originally contained in two loose-leaf note books. Notes pasted on the front covers explain that one volume was given by Jerome's widow, Lucy Mix Day, to Henry L.V. Day on September 4, 1962, and the second passed to Henry from Lucy's estate on May 31, 1969. The contents of the first volume are classified as "Miscellaneous," "Labor Conditions," and "Code File." They relate to the economic development of north Idaho, the effect on the mining industry of recent and proposed legislation, the North Idaho Chamber of Commerce, and the North Idaho Press Association, industrial insurance, taxation, the market for mining stock, metal production and prices, appointments of public officials, the drafting of mine employees for military service, activities of labor unions - particularly the I.W.W., and of labor organizers, reports of local gossip about members of the Day family, labor legislation and labor advisory boards, planning for strikes, and arrests of I.W.W. members. The contents of the second volume relate entirely to activities of the Democratic Party in Idaho and actions in the state legislature. Contents of these two notebooks were removed and placed into file folders.

The two miscellaneous items are a carbon typescript titled "Report of Labor Troubles by Operators and McWade, June 1919," which consists of transcripts of meetings held in the office of Jerome Day between Robert M. McWade, U.S. Conciliation Commissioner, and local mine operators on June 25, 27, and 28, 1919, and a printed "Brief of Defendant in Error" in the C. Fred Kratzer vs. Jerome J. Day case in 1926.

The second series consists of personal financial records including 2 ledgers and 15 voucher registers.