Carlyle Buley's book, The Old Northwest: Pioneer Period, 1815–1840 (Indianapolis: Indiana Historical Society, 1950), a two-volume work that won a Pulitzer Prize. Thornbrough's editing projects, either alone or with fellow historian Dorothy Riker, resulted in the publication of several scholarly research tools that included Journals of the General Assembly of Indiana Territory, 1805–1815 (Indianapolis: Indiana Historical Bureau, 1950), Indiana Election Returns, 1816–1851 (Indianapolis: Indiana Historical Bureau, 1960), and three volumes in the governors of Indiana series (James B. Ray, Noah Noble, and Samuel Bigger). After Indiana archaeologist Glenn Albert Black died in 1964, leaving behind an uncompleted manuscript of his work at Angel Mounds, Thornbrough commissioned others to finish Angel Site: An Archaeological, Historical, and Ethnological Study (Indianapolis: Indiana Historical Society, 1967) and edited the final manuscript to assure continuity of style. When the set of illustrations was stolen while they were in the printer's possession, Thornbrough secured replacements for 420 photographs and determined their placement in the book. Thornbrough left the IHS staff in 1967, when she went to work for the Library of Congress in Washington, D.C. She spent twenty months as a specialist in early U.S. history in its Manuscript Division. During Thornbrough's absence from Indianapolis, the IHS reorganized to establish a leadership role for her. She returned to Indiana in 1968 and began an eight-year tenure as the IHS's director of publications and library. One of Thornbrough's major editing projects was leading a project team to publish The Diary of Calvin Fletcher (Indianapolis: Indiana Historical Society, 1972–1983). Fletcher, a prominent Indianapolis resident, began his diary in 1820 and continued the effort with some periodic gaps for nearly twenty years. Reviewers commended the nine-volume work for its editing. Thornbrough was appointed the IHS's first executive secretary in 1976, following its reorganization as a separate entity from the Bureau, a state-supported historical agency. As an administrator and editor for the IHS, Thornbrough encouraged major historical research projects, funded a history of medicine position at Indiana University, released the album Indiana Ragtime (Indianapolis: Indiana Historical Society, 1981), and supported the publication of the IHS's black history newsletter and its collection program in African American history. Thornbrough also encouraged efforts to microfilm Indiana newspapers. She retired from the IHS in September 1984. Death and legacy Thornbrough died on November 8, 1999. A memorial tribute appearing in the Indiana Magazine of History in 2000 described her as "one of the most