Hertfordshire Half Marathon 2026

The Hertfordshire Half Marathon starts and finishes before Knebworth House, a Grade II listed house near Knebworth in Hertfordshire. It is an autumn closed-road half marathon with a 10K option on the same race programme, chip timing, a 9:00 AM start, and a three-hour limit for the half marathon. The route uses rural roads and countryside paths around Knebworth Park, with rolling sections rather than a completely flat run. It draws runners chasing a personal best as well as first-timers moving up in distance, and the event supports Garden House Hospice. The setting adds local character: Knebworth House sits in large gardens and parkland, has hosted major open-air concerts by acts such as Oasis, Led Zeppelin, Robbie Williams, and Red Hot Chili Peppers, and also has visitor attractions including an adventure playground and dinosaur trail.