A map of the Santa Clara County Fairgrounds is below:
The Fairgrounds is located at 344 Tully Road (at South 7th Street) in San Jose.
In fact, the 26 bus stops within a few feed of the main entrance of the Fairgrounds on Tully Road. From VTA light rail, transfer at Curtner light rail station to any Eastridge-bound 26 bus and get off at the Fairgrounds entrance on Tully road.
From downtown San Jose to the Fairgrounds, catch a Kaiser San Jose or Gilroy-bound 66, 68, or 568 Rapid bus respectively at 2nd & Santa Clara, then get off the bus at Monterey Highway & Tully/Curtner. Afterward, walk or bike about 1/4 mile east on Tully to the Fairgrounds.