The law will cost more than $5 million a year for the treatment of about 120 patients.
Michael Sitton held up before and after photos of his 31-year-old daughter Tiffany, who he said has struggled with mental health problems for years and refuses treatment.
"This girl could be saved," he said.
Sitton was among nearly 20 people who stood before the Orange County Board of Supervisors. More than half supported Laura's Law, which allows court-ordered outpatient treatment for people with severe mental illness who meet a long list of criteria.
"They must have a history of a lack of participation in needed mental health treatment, and we must show that the person's condition is substantially deteriorating," said Mary Hale with the Orange County Healthcare Agency.
Officials say in addition to not complying with treatment, the person's mental illness has to lead to two psychiatric hospitalizations or jail time within the previous three years.
Laura's Law was first adopted by state lawmakers in 2002 with the condition that each county approves its own program. Up until now, Nevada County was the only one that had fully implemented it.
The law received more focus after the death of Kelly Thomas, a 37-year-old man who suffered from schizophrenia. He died in 2011 after a run-in with Fullerton police.
"It would not have saved Kelly that night, but it may have kept him off the streets to begin with," said his father, Ron Thomas.
But others say the law erodes civil liberties.
"You are not incompetent to make decisions and they can force treatment on you, and this is why this is very dangerous," said Ann Menasche, a disability rights California attorney.
Ron Thomas says his son's mental illness prevented Kelly from making rational decisions about his health. Laura's Law would have given his family the ability to get him treatment.
"There were time periods where I could not be on top of him to make him take his meds that he went downhill," said Ron Thomas.
Under the law, no one can be forced to take medication. A hearing can be called every two months to decide whether treatment should be continued.
The program is expected to begin in October.