The Clay County Fair is held every September in Spencer, Iowa, United States. It is the largest county fair in the state of Iowa. It has the largest agricultural exposition in North America. Bringing in over 310,000 visitors a year, the Clay County Fair is one of the largest county fairs in the United States. 2011 set attendance records of 328,000. Beginning in 1918, the fair has grown considerably over the past near century. In its first year the Clay County Fair brought in 30,000 guests.