King died at the hands of a convicted sex offender who buried her body in a shallow grave in San Diego.
John Gardner pleaded guilty to King's murder and is serving a life sentence without the possibility of parole.
Chelsea's family is hoping to take this tragedy and use it to help prevent other families from feeling and loss they are going through right now.
"You have to choose hope and you have to be an agent for change, that's what our daughter would ask of us," said Brent King, Chelsea's father.
Chelsea King would have turned 18 last month, and she likely would have started college this week. Instead, her family is marking a bitter sweet victory in the California legislature and vowing to bring their cause to other states, including Illinois.
For Kelly and Brent King, life without their daughter is a day to day struggle.
"We're learning every day how to navigate our new life. It's not getting easier, we're just learning to steer through the days," said Kelly King.
It was six months ago today that Chelsea's body was discovered near San Diego. She had been raped and murdered while out jogging by a registered sex offender who had broken parole and, unbeknownst to police, had killed another girl one year earlier.
"The way our daughter was taken only spoke to one thing. It was a preventable issue," said Brent King.
Since then the Kings have become outspoken advocates for tougher laws against sex offenders, including a mandatory life sentence for some first-time child predators.
On Tuesday, a bill they spearheaded in California named Chelsea's Law passed a crucial vote in that state's senate.
"I had tears streaming down my face. I was so, so very proud," said Kelly King.
After three years in California, the Kings, earlier this summer, returned to Naperville where they had previously lived for ten years. It was less a move than a search for the familiar and a chance at a fresh start for their 14-year-old son Tyler.
"In San Diego, Tyler is known as Chelsea's brother. Here, Tyler can be Tyler," said Brent King.
"Even the simplest things in life will be altered by our pain and our grief. We don't recognize each other. We don't recognize ourselves," Kelly King said during a statement in court in May.
When asked if returning to Naperville has helped, she said, "it's been a tremendous comfort. We've been so blessed in so many ways.
"Chelsea was running towards becoming a marathon runner. And she continues to let us know, 'hey, great job in California.' That was our test, right? We're going to keep running," said Brent King.
"This is our marathon," said Kelly King.
The Kings have started a foundation called Chelsea's Light, and their Facebook page has almost 100,000 supporters. They say they plan to work on get-tough legislation against child predators in Illinois, just like they did in California. Their first priority is to get settled in Naperville. Their son Tyler started high school this week.