O’Halloran received hundreds of letters during her years in the legislature, most of them business-related material from constituents, colleagues, and lobbying interests. She also retained copies of her responses to some of her incoming mail. Save for a few letters from 1970-1972, all of the correspondence here was written in the years 1973-1978. There is some correspondence that was neither written to or by her. Most of these are letters between fellow legislators. All correspondence is arranged in chronological order by date, without regard to correspondent or topic, and filed in folders labeled by year and month. Letters for which a date could not be determined were placed in undated folders, which are filed before the dated folders. No envelopes have been retained.