Boulder County was one of the original 17 counties of Colorado created on November 1, 1861. The county was named after the city of
Boulder, which, along with Boulder Creek, was named after the abundance of boulders in the area (go figure). Boulder County's borders have
changed relatively little since, with the exception of a subtraction of territory from its southeast corner when the City and County of
Broomfield were created in 2001. The county seat and largest city is Boulder.
Source: wikipedia.org