[3] He was one of six founders, collectors and dealers, of the Museum of Early American Folk Art in 1961;[1] the others were Adele Earnest, Cordelia Hamilton, Marian Willard, Burt Martinson, and Arthur Bullowa.
[1] In 1968 artists and collectors Michael and Julie Hall introduced Hemphill to Edgar Tolson, a meeting which he would later describe as an epiphany.
Its result was that he began to consider purchasing the work of living folk artists for his own collection, which grew in its ethnic and national diversity.
Artists represented in his collection of nearly 3,000 items included Martín Ramírez, Howard Finster, Jon Serl, Bessie Harvey, Sister Gertrude Morgan, and Joseph Yoakum.
[4] 1989 saw him become one of the founding members of the national advisory board of the Folk Art Society of America, a position he occupied until his death.
[2] Two of his own artworks reside in the collection of the Smithsonian American Art Museum, a Portrait of Hermine Katz, Atlantic City, of 1949[5] and a Chandelier of unknown date.
[1] Another portrait of Hemphill, by Malcah Zeldis and dated 1990, is in the collection of the Abby Aldrich Rockefeller Folk Art Museum.