The Leonard Fierro Papers (1927-1995) document Fierro's work as an educator, activist and advocate for bilingual education. The majority of the material dates from the early 1960's through 1970's, with very sparse documentation of the 1950's. These files illustrate Fierro's development of bilingual education teaching materials for San Diego County. His papers include reports, correspondence, teaching supplements, newspaper clippings, and audio cassettes. Highlights include materials relating to the efforts of the National Origin Desegregation Assistance Center (NODAC or Lau Center) in the Institute for Cultural Pluralism and personal correspondence during his military service through WWII. The collection consists of four series: Professional Files (1964-1992), Personal Files (1935-1995), News Clippings (1950's-1995), and Book Project Files (1927-1995).

The Professional Files (1964-1992) are divided into two sub-series, Education (1964-1990) and Organizations (1964-1992). These files document Fierro's work as an advocate for bilingual education primarily in San Diego during the 1960's and 1970's, and his membership and association with multiple educational and community organizations. The Education sub-series, alphabetically arranged, includes teaching supplements as well as reports and publications documenting his work and  research concerning the development and implementation of a language-sensitive curriculum for English-learning students. These materials include bilingual lesson plans for Spanish-speaking preschool students as well as school integration reports from across the country from the U.S. Commission on Civil Rights. Also alphabetically arranged, the Organizations series documents Fierro's affiliation and participation with local and national groups that shared his outlook on bilingual education. Among these groups are the Chicano Federation and Association of Mexican-American Educators. This sub-series includes correspondence, memorandums, and reports released by the various organizations.

The Personal Files (1935-1995), document Fierro's time in the military and his family life. A large portion of the material dates from the 1990's, after Fierro's retirement, and focuses on membership materials to the San Diego Historical Society and National Timberwolf Association, "an association of World War II Veterans of the 104th Infantry Division, U.S. Army." The series also contains alphabetically arranged correspondence, resumes, and photographs of Tolteca Athletic Association reunions. The majority of correspondence are letters Fierro exchanged with family and friends while serving in the Army during WWII. Letters were addressed to Fierro while in Camp Roberts, California in 1944 and to Luxembourg and Belgium in 1945. Also, included is an order from general headquarters for his award of a Purple Heart for wounds while in Germany.

The News Clippings (1950's-1995) series exhibit Fierro's research interests especially in education, local politics and racial discrimination. They are arranged alphabetically by subject and include articles from the San Diego Union Tribune, L.A. Times, The New Mexican, San Diego Free Press, and other newspapers documenting varied issues from local student enrollment statistics to the murder of local Black Panther Party member Sylvester Bell in 1969. The majority of the files date between the late 1980's and early 1990's with particularly few clippings from the 1970's.

The Book Project Files (1927-1995) document Fierro's research for an unfinished manuscript that would highlight local Latino activists. The series consists of audio cassettes, notes, articles, interview questionnaires, and photographs, all of which are alphabetically arranged. The records cover topics such as Camp Oliver, Neighborhood House, the Tolteca Athletic Association, and the post-WWII period. The cassette tapes contain interviews of individuals such as David and Mary Naranjo, Natalie Coronado, Raul Almera, and Totleca founder Frank Peñuelas.