The woman apparently walked into the local sheriff's station Saturday and filed a complaint regarding the incident she claims took place Thursday night.
Authorities say they can only confirm there's an investigation into the allegations. The 25-year-old actress was not arrested or detained.
Lohan's publicist questions the validity of the woman's claim since she waited two days to file the complaint and allegedly called the media before police.
Lohan's strict probation for a 2007 DUI case in Beverly Hills finally ended last month after a judge said she successfully met all the terms of her probation.