Efren Carrillo was born in North Hollywood in Los Angeles, California, and moved to Mexico City, Mexico at the age of one. He was raised in Santa Rosa, California, where he lived off West Ninth Street. He graduated from Santa Rosa High School in 1999, and graduated from UC Berkeley in 2003 with a bachelor's degree in environmental economics and policy.
After graduating from UC Berkeley, Carrillo moved back to Sonoma County, where he became a project coordinator for the Sonoma County Economic Development Board designing policies. Carrillo progressed into the banking industry where he became education and government relations manager for Redwood Credit Union. In 2007, he was recognized by the North Bay Business Journal as being one of the 40 business and community leaders under 40.
In November 2008, Carrillo was elected to the Sonoma County Board of Supervisors at the age of 27. The term ended on June 2012, and Carrillo was re-elected to be on the Board of Supervisors in January 2013. He represented the 5th District, which spans across entire Sonoma County coast, the lower Russian River area, Sebastopol and the west and southwest Santa Rosa areas extending in to Highway 101.
On May 6, 2014, the Sonoma County Board of Supervisors unanimously criticized Carrillo after refusing to resign after his testimony in his peeking trial. Carillo testified that he had broken open a woman's screen window at 3am wearing only his underwear in an attempt to have sex with the victim. However, no formal censure resolution was introduced.
Carrillo serves on the Santa Rosa Gang Prevention Task Force, Health Action Sonoma County, the Board of Directors for the Center for Volunteer and Nonprofit Leadership of Marin, Habitat for Humanity of Sonoma County, and was president of the board of the Southwest Community Health Center.
On September 5, 2012, Carrillo was arrested at a nightclub in San Diego, and was booked on charges of misdemeanor battery and disturbing the peace. He was involved in a fight that took place that at the nightclub, and another man was seriously injured. Carrillo posted bail the same day. Charges against Carrillo were dropped in October 2012.
On the morning of July 13, 2013, Carrillo was arrested in Santa Rosa on charges of burglary, a felony, and prowling, a misdemeanor while clothed only in underwear and a pair of socks. He was released the same day after posting $40,000 bail. He released a statement in which he attributed his attempt to break into a woman's bedroom due to alcohol and he immediately entered a rehabilitation center. On October 31, 2013, Carrillo was formally charged with misdemeanor peeking in connection with the incident. On April 28, 2014, he was found not guilty of attempted peeking.