Running is the heartbeat of Boulder — one of the three hallmark recreational activities of our community (along with cycling and hiking, of course).

Together, we run the streets & trails of Boulder, and serve as one of the great training grounds for Olympians, world-class athletes, and leisure runners alike. We are so grateful & proud to have the world's best 10k — but despite running being hardwired into Boulder’s DNA — we had no signature city marathon. This was the question we asked everyone — and we couldn’t find out why.

In one of the great health meccas of the US, rated one of the healthiest, happiest cities in the country, we couldn’t find a premier, signature marathon.

After years in the making and the opportunity to acquire a 19-year-old race series, the Boulder Backroads Marathon & Half Marathon, we knew the time was now. As residents of Boulder County and local business owners, our goal from day 1 has been to create an inspiring, community-driven marathon series to serve as the premier fall race in the state. We decided to create the epic, downtown marathon race the beautiful city and community of Boulder deserves.

Boulderthon® was born.

Boulderthon 2023 will take place on Sunday, October 8th 2023. The top-rated, fast-growing race series became the second largest marathon series in Colorado in its first year of existence, and the largest fall running event in the state.

Tucked into a picturesque valley below the iconic Flatirons, Boulder, CO sets the backdrop for the top-ranked, signature Boulder Marathon, Boulderthon. Boulder is a world-class destination offering 300 days of sunshine and endless recreation, shopping, dining, cultural and entertainment choices. It's no wonder National Geographic named Boulder the Happiest City in America.

In its second annual edition, Boulderthon drew runners from all 50 states as well as 15 countries, as the signature marathon showcased the world-class city of Boulder set at the foothills of the spectacular Flatirons.

In 2023, Active named Boulderthon as one of the Top 5 Best Half Marathons in the United States.

“Racing in Boulder, Colorado, should be on every runner's bucket list, and the Boulderthon Half Marathon might be the perfect way to cross it off. The gives you a true sense of Colorado's scenic beauty. as you run along the backroads, the foothills of the Flatirons and into Downtown Boulder to finish on the historic Pearl Street Mall. Veteran runners have touted this as one of the best race events of their lives; it has all the amenities of a big race (gear check, pace groups, plentiful aid stations) with the charm and attention to detail of a small race. Plus, it's a downhill finish!”

After nearly tripling in size last year and selling out, Boulderthon has instituted a new 5,000 runner cap this year and is expected to sell out again.


Boulderthon Marathon Reviews


I've run nearly 50 marathons and/or half marathons and this ranks among the very best. Race day execution was flawless and I echo the previous comments about the professional staff and well organized volunteers groups. Looking forward to next year already!


"Great Day, Great Race. I can’t imagine a marathon that is run any better. Everything went well, volunteers were plentiful and helpful, aid stations were great, and the weather was perfect for a long run. And Boulder turned out in force to cheer us on."


This was by far one of the best races I’ve participated in - Aid stations were dispersed well and there was so much help and encouragement from the volunteers and police officers. Thank you thank you thank you.


Fun course, positive vibes, beautiful views and just enough support along the way. Thanks to all who helped make this race happen. I’ll be back every year. Perfect Race.


"This was my 1st half marathon race and I had a blast! Everyone was in a great mood and the course was beautiful! Thank you all!"


"Fantastic Race. Great job to all who organized this event. You knocked it out of the park! From the great communications, well organized packet pick ups, friendly aid and water stations, and after party."


"Terrific race, beautiful course. Staff and volunteers were first class all the way!" 

95% of runners would recommend to their friends, with #1 reason being Downtown Finish & Course Views.