On Sunday, up to 25,000 people are expected to watch as around 15,000 runners race through Newport Beach, Santa Ana and Costa Mesa.
Organizers said in an e-mail that around 827 of those are from Newport Beach and 544 are from Costa Mesa.
Some of those are from the Junior League of Orange County, a women's philanthropic group.
For the first time, the Junior League is partnering with the O.C. Marathon to raise funds for its programs, which include perinatal depression awareness and charity work with foster-care kids.
Stephanie Lincoln, co-chairwoman of the organization's O.C. Marathon committee, said there will be 75 Junior League runners and about 30 volunteers working water stations. The group's involvement has helped them raise more than $3,800 so far.
The Junior League running team also includes a dash of celebrity: Jennifer Glava, the current Mrs. California, will run the 5K.
"Being involved with the community is the reason I chose both to compete in the Mrs. California Pageant and to join the JLOCC," Glava said in a statement. "Running has become an important part of my fitness program, and supporting the League's effort in this way is a natural for me."
The Junior League will also host an after party from noon to 4 p.m. Sunday at Aloha Grill on Newport Boulevard, where a $10 donation will get guests food and drink specials.
Other charity partners include the American Cancer Society and Train 4 Autism.
More than 43 streets have been closed to accommodate the marathon, which starts at the Newport Beach Marriott and winds up past John Wayne Airport, west on Segerstrom Avenue and down through Fairview Park, ending at the OC Fair & Event Center.
A spokeswoman said Friday that 120 marathon spots, 600 half-marathon spots and 400 5K spots were still available. Online registration is closed. To register, visit the Active Lifestyle Expo.
If You Go
What: Seventh annual OC Marathon.
Where: The starting line is at Newport Beach Marriott, 900 Newport Center Drive.
When: The full marathon starts at 6 a.m. Sunday.
For more information, including road-closure information and parking details, visit ocmarathon.com.