District attorney's spokeswoman Jane Robison says Bynes entered the plea Monday through her lawyer. The actress was sentenced to three years of probation and three months of attending alcohol education classes.
Bynes was arrested in April of 2012 on suspicion of drunken driving after the cruiser was hit in West Hollywood.
The 27-year-old actress already is on probation for driving with a suspended license. She received psychiatric treatment last year after authorities said she started a fire in the driveway of a Ventura County home.
Bynes also was ordered to get counseling after she allegedly threw a bong out of a Manhattan window last year.