With more than 27,000 participants, this will be the biggest turnout yet for the Detroit Free Press/Talmer Bank Marathon.
The event is international, allowing runners to cross into Windsor and back.
"It's unique," said Barbara Bennage, the executive director. "We cross over the Ambassador Bridge and Canada, and through the Detroit-Windsor tunnel. It shows off our city our unique neighborhoods."
About $2 million will be raised for more than 70 different charities and every runner, has a story.
"In 2009 I weighed over 400 pounds," said Missy Smith. "I started losing weight - I just started walking, and then I met this group called MRTT. It's Moms Run This Town and it's the Downriver chapter."
Smith found her passion for running and for her new friends - while shedding more than 200 pounds. Since then she's participated in many runs, but the Free Press Marathon is her favorite.
"I just loved it. the people are great, the volunteers were amazing," Smith said.
Missy won't be able to run this year after injuring her knee and having gull bladder surgery. Instead, she won a competition to hold the finish line tape for her friends.
"I'm going to do it in honor of a lot of different people, Missy's going to be there waiting for me and I can't wait to see her at the finish line," said Crystal Lobato.
"Having your friends, just knowing they're out there supporting you, waiting for you, to give you a hug," said Kelly Prather. "Is part of why we do this."
For the group, this year will be especially difficult after the passing of one of their members.
"Our friend Amanda Tackett, who passed away a couple months ago," Smith said. "She would've wanted to run this race, so I'm there supporting these girls just like she would have."
And even though she isn't running, This year's race means more to missy than any other.
"This is our favorite," Smith said. "They supported me and I feel like they're my sisters."
The race starts at 7 a.m. Sunday and again it's expected to be the most crowded yet, so plan on getting here early.