Can someone obtain a copy of there's birth certificate if they were born in Mexico but is a resident of sonoma county? And if so what is needed to bring in to the office and fees? Thank you

You have to go to the county you were born in to obtain birth records in the US. Policy may be different in Mexico. Still would be local records.

The Sonoma County Clerk only has records for people born in Sonoma County. To obtain a copy of their birth certificate they can contact the Consulate for further assistance on how to obtain their birth certificate if they were born in Mexico.