The Diocese of Santa Rosa in California comprises Del Norte, Humboldt, Lake, Mendocino, Napa and Sonoma Counties.

The first Catholic presence in the area was the establishment of the Mission San Francisco Solano in present-day Sonoma in 1823 by Jose Altamira.

[2] In 1828, a Native American woman was listening to Juan Amoros preaching to a group by a creek near present-day Santa Rosa.

[8] Ziemann submitted his resignation as bishop of Santa Rosa to the Vatican in 1999 after admitting a sexual relationship with a man and being sued by him.

[13] In 1996, Reverend Gary Timmons was convicted on charges of committing lewd or lascivious acts with children and sentenced to four years in prison.

[13] In August 2006, the Sonoma County, California, Sheriff's Office recommended criminal charges against Bishop Walsh for not reporting multiple child molestations by Reverend Francisco Ochoa.

Walsh immediately suspended Ochoa but failed to report these crimes to police during the five-day time period mandated by law.

The Sonoma County District Attorney's Office eventually approved a plea agreement for Walsh, which called for four months of counseling in lieu of prosecution.

[18] In March 2023, the Diocese of Santa Rosa filed for Chapter 11 bankruptcy amid numerous sex abuse cases.