Katharine Martindale, the last member of a long established, active and prominent La Crosse family, was born 6 January 1890 in La Crosse. She was the middle child of Sophie and Stephen Martindale IV. After graduation from La Crosse High School in 1908 she attended Smith College in Northhampton, Massachusetts, graduating in 1912. She then studied home economics at the University of Wisconsin at Madison from 1913 to 1915 before teaching, first at Baker University (Baldwin, Kansas, 1915-1916) and then at the University of Washington (Seattle, 1916-1917). In 1917 her mother had serious surgery, and Katharine returned home to live with her parents. Shortly thereafter she resumed her studies at the University of Wisconsin, earning her Master of Arts in home economics in 1921. Around this time she appears to have started working in her father's insurance business as an agent for the Massachusetts Mutual Life Insurance Company. After her father's death in 1923 Katharine carried on the business, becoming an agent for the Detroit Fire and Marine Insurance Company, which recognized her for twenty-five years of service in 1948. In 1950, she transferred her office to the Martindale home at 10th and Cass Streets so that she could be more attentive to her ailing mother. The fire insurance portion of her business was sold in January 1955 to the Holly Company, and Katharine became a certified life underwriter for the Northwestern Mutual Life Insurance Company, the firm with which her father and grandfather had been primarily associated. She retired in 1969.

Throughout her life Katharine was involved in the La Crosse community. Her family had been associated with the First Congregational Church since the mid-1800s, and Katharine herself was an active member until the time of her death. At various times she belonged to different clubs and social and cultural groups such as the La Crosse Country Club, the American Association of University Women, the La Crosse Garden Club, and the State Historical Society. During the 1950s she worked with several conservation groups to preserve certain wildflower areas for scientific study. Katharine had a longstanding interest in antiques, historical sites, old books, and family history. Toward the end of her life she was intensely interested in restoring and preserving the family home, which three generations of Martindales had occupied, and in distributing family furniture, jewelry, dishes, linens, and antiques. Shortly after her death, in La Crosse on 13 October 1977, the house was listed with the National Register of Historic Places, and it was later sold under a protective covenant. A copy of her obituary may be found in the series Genealogical Materials.

Family correspondence consists of letters from Katharine to her parents, brother and sister, and her brother's children. Most of the correspondence is from Katharine to her parents and dates from 1908 to 1917, that is, from her college years to the end of her working years away from home. Katharine wrote home at least once a week, and the letters reveal many details about the daily life of a college girl and young working woman of the times. The only correspondence found here to her sister Henrietta is from the years Katharine was at Smith. All later correspondence to Henrietta as well as that to her husband and children is filed in the Henrietta Martindale Hyessa Wilson and Family series. The correspondence to Stephen V and his family concerns family matters and the distribution of furniture, china, linens, and other contents of the family home. The correspondence entitled Relatives and Friends consists of letters to Katharine (and sometimes to her mother as well) from friends and relatives who were frequent correspondents; arrangement is alphabetical by writer. There are occasional copies of Katharine's replies in some folders.

Correspondence with relatives, especially Lois and Wallace Martindale, discusses family genealogy; the Laverty file contains information about the house and its original owners; and the folder for Jens Jensen, an associate of Frank L. Wright, includes his plans for developing Martindale property near the Indiana Dunes. The grouping Miscellaneous Friends and Acquaintances consists almost solely of incoming letters from persons with whom Katharine infrequently corresponded. Included are letters from college friends, expressions of sympathy, news regarding events in her friends' lives, thank you letters, and so forth. There is one slim folder of copies of Katharine's outgoing letters. Where last names are not given, first names determine alphabetical order.

The second sub-series, Business Papers, 1914-1977, is divided into Insurance Papers and Personal Business Papers. The single folder of insurance papers primarily contains miscellaneous correspondence with insurance companies and copies of contracts. Some correspondence relates to Katharine's decision not to represent Northwestern Mutual Life Insurance Company immediately after her father's death. Personal Business Papers consist mostly of correspondence. The files for attorneys are for the most part letters to and from Katharine concerning her will and the eventual settlement of her estate; copies of her different wills are to be found in the folder labeled Wills and Testaments. Other files of interest are La Crosse County Medical Society, which contains information about area medical history; Midway Prairie Scientific Area and State Board for the Preservation of Scientific Areas; and Miscellany. The Midway file contains correspondence, clippings, articles, etc. about the preservation of the pasque flower and the establishment of the Midway Prairie Scientific Area. The Miscellany folder consists of correspondence to and from institutions and businesses and includes early correspondence with colleges and universities concerning teaching positions; orders to out-of-town merchants for shoes, clothing, and personal items; information requests and responses; correspondence with miscellaneous attorneys regarding legal matters and her will; and so forth.

In her later years Katharine's major concerns and interests centered about the preservation and restoration of the family home and its contents. The sub-series House and Contents, 1919-1977, reflects her efforts in these endeavors and also reveals much about Katharine herself. The papers are divided into General and Subject sub-series. The former consists almost exclusively of correspondence and are arranged chronologically and alphabetically thereunder. The latter, which are in alphabetical order by subject, are made up primarily of correspondence. The correspondence in both General and Subject folders deals with repair and restoration of the house and its contents; identification of antiques and determination of their value; attempts to donate or sell antiques, books, and documents; and her efforts to settle the future of the house itself. This correspondence incidentally provides additional information about the Martindale family and local history. The Historical Information file is particularly noteworthy because it includes several histories written by Katharine of the home and family. The folder Bills and Receipts contains household bills, some of which reflect repairs done to the house and contents. The household bills of Stephen III and IV include similar items and they should be consulted for information about work done on the house prior to the early 1920s. Miscellany includes pamphlets, printed information, and a few samples which Katharine gathered to help her make decisions for her restoration projects. The series Maps and Documents should be consulted for the original deed to the house and several floor plans which appear to be for the home and other buildings on the lot at 10th and Cass.

Katharine's School Papers, 1901-1929, include reports cards and program announcements from public school and college as well as course papers and materials from university classes which Katharine both took and taught.