The Walnut branch of the Los Angeles County Public Library System is open five days a week, Tuesday through Saturday. The library, located on La Puente Road, is the only public library within city limits. The library has a collection of more than 100,000 books and offers free Internet service.
The Walnut/Diamond Bar station of the Los Angeles County Sheriff's Department provides police services to approximately 45 square miles in the cities of Walnut and Diamond Bar. Officers use civilian volunteers to help patrol traffic and parking violations and to help with administrative tasks at the station. The station's Explorer Program allows teens and young adults from ages 15 to 21 to assist at the station and ride along with officers to explore careers in law enforcement.