Gregory Ahern was born in Oakland, California, and is a lifelong resident of Alameda County. He graduated from Moreau Catholic High School in Hayward in 1975. He went on to earn a bachelor’s degree in Economics and Business Administration from Saint Mary's College in Moraga. Sheriff Ahern was hired as a Deputy Sheriff in 1980, was promoted to Sergeant in 1986, promoted to Lieutenant in 2000, promoted to Captain in 2003, promoted to Commander in 2005, and promoted to Assistant Sheriff in 2006. On June 6, 2006, Gregory J. Ahern was elected Sheriff and became the 22nd Sheriff of Alameda County on January 8, 2007.

Sheriff Ahern has been actively involved in the development and implementation of a  number of programs that have proven to be highly beneficial to the citizens of Alameda County, including the Youth and Family Services Bureau, Drug Education and Enforcement programs, Cold Case DNA Unit, D.U.I. Enforcement Unit, and coordinator of the Strategic Planning process for the future health of the organization. Sheriff Ahern also initiated the Urban Shield tactical training exercise that provides a training venue to several thousand first responders each year. The focus is to test the skills, tactics, and equipment of the participating tactical teams, as well as first responders' regional ability to coordinate and sustain law enforcement, medical, and emergency services in the event of a large-scale terrorist attack or natural disaster.

https://www.alamedacountysheriff.org/about-us/sheriff-bio