The early 1900's brought slow and steady growth to the Boulder County Fair as permanent buildings replaced the tents at Roosevelt Park one by one, with some costs being borne by the City of Longmont. In 1921 a record breaking crowd of 2500 attended the opening day. The fair prospered.
Only one break in the continuity of the Fair occurred when it had to be cancelled in 1946 because of the polio outbreak. But ultimately, with the continued success of this great community event, more room and better facilities were needed. In 1976, the County Commissioners purchased the Affolter Corner Farm, 130 acres of land at the northeast corner of Nelson and Hover Road. In the fall of 1978, the Fair opened in its present location in the first building at the new complex, which would be completed over the next 15 years.