Boulderthon powered by lululemon has announced that its marathon and 10K distance races have officially sold out for the 2026 event on September 27, 2026 in Boulder, CO.
Limited entries remain across the remaining distances, including the 5K, half marathon and Kids Run, with those categories also reported to be approaching capacity.
Established in 2021 as a non-profit community running event with 1,600 participants, Boulderthon has grown to host over 17,000 runners for its 2026 edition. The weekend of events attracts participants locally from across Colorado, as well as nationally and internationally.
Phil Dumontet, Founder of Boulderthon, said “Selling out several distances and nearing capacity across the entire event is an incredible milestone for Boulderthon and for our community. When we launched Boulderthon in 2021, our vision was to create a world-class running experience rooted in Boulder. The growth we’ve seen since then has been extraordinary, and it is a reflection of the runners, volunteers, partners and community members who continue to believe in this event.”
The 2026 event schedule includes the marathon, half marathon, 10K, 5K and the Boulder Country Day School Kids Run. In its fifth year, the event generated an estimated US$13.9 million in economic impact locally and regionally. The marathon distance serves as an official Boston Marathon qualifier and is a USATF-sanctioned event.
Operating as a 501(c)(3) non-profit organisation, Boulderthon also engages in local infrastructure initiatives. Through a partnership with the PLAY Boulder Foundation, the organisation is contributing US$50,000 toward resurfacing the parking lot at Tom Watson Park, installing a new water fountain and upgrading park landscaping.
Boulderthon has pledged to match additional community donations through December 31 up to a further US$50,000, bringing its potential total funding contribution for the park project to US$100,000.
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