Registration for the Bank of America Chicago Marathon officially opens Tuesday, but Monday night, some runners got a jump on the process.
It's never too early to start training -- especially if joining in a fun run gets you a chance to sign up early to get one of the coveted spots before registration opens to the general public.
A couple hundred runners took advantage.
"Marathoning, I think, must be getting more and more popular -- you keep thinking it's peaked, and it hasn't... it's a great challenge," said runner Tom Osran.
"The reward comes at the end -- when you cross that finish line, you think -- wow, I did this," said runner Nadia Waterman.
This will be the 36th Chicago Marathon, but in the last few years, the popularity has exploded. In addition to the 45,000 runners, the race attracts an estimated 1.7 million spectators and brings more than $200 million in economic impact to the city.
Three years ago, the marathon sold out in 51 days. In 2011, they reached the limit in 31 days. Last year, it took just six. Marathon Director Carey Pinkowski is predicting this year will fill up even faster.
"It's a world class event in your backyard, which is amazing," said Pinkowski.
The race also attracts some of the world's best runners, including three-time Olympian Dathan Ritzenhein, who gets the first entry.
"It's one of those marathons now that people really, they got to do, it's on their bucket list," said Ritzenhein.
Marathon popularity is not limited to Chicago - suburban Naperville will host their first marathon in November. They opened registration a few weeks ago, and closed it to 3,200 runners just 14 hours later.
All interested runners can register at ChicagoMarathon.com.