The Percival Gallagher Papers document the personal and professional life of prominent landscape architect and partner of the Olmsted Brothers firm. In addition to research materials collected over the course of his life, Gallagher saved memorabilia from all aspects of his life, from handwritten notes about landscapes and gardens to travel souvenirs.
In 2015, the IMA Archives digitized all of the photographs and select manuscript material from Gallagher's papers. The digitized collection has been made available online through the Indianapolis Museum of Art’s Digital Archives Portal.