Registration for Boulderthon 2023 is now open! After nearly tripling in size and selling out last year, Boulderthon has instituted a new 5,000 runner cap and is expected to sell out again this year. Register today.
aerial view of Boulder streets


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 have 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 Saturday, October 7th and 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 course starts at Boulder Reservoir, which gives you a true sense of Colorado's scenic beauty. Then you run along the foothills of the Flatirons. Finally, you wind your way into downtown Boulder and 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.