Dogs are not allowed in the Sonoma Plaza park, with the exception of service animals. Outside the park there are many businesses around Sonoma Plaza that are Dog Friendly.
There is a small dog park located near the Community Meeting Room (175 First St. West)
However, dogs are not allowed in the Plaza’s Park. There is a $100 fine.
Check out this list of Dog Friendly Places by Sonoma Valley Dog Owners and Guardians