In 1917, the Clay County Fair Association was organized. The first modern Clay County Fair was held in 1918, just six weeks before the Armistice of World War I.

In an article in the April 3, 1918 Spencer Daily Reporter, it was reported that preparations for the upcoming fair were being made with the race track being nearly completed.  The same article included the fact that soon work would start on the two ornamental entrance ways to the fair grounds. The entrance ways were to be built in the shape of an arch with towers at each side. Ticket booths were to be built in connection.

Held September 24-27, the 1918 Clay County Fair was the largest county fair held in Iowa that year, drawing more than 30,000 people and taking in a total gate receipt of $16,000.

With the success of the 1918 fair behind them, the Clay County Fair Association in November wasn’t asking if they could offer a fair as good as the one just completed, but rather was making plans for a bigger and better county fair.

Secretary M.E. Bacon urged farmers to exhibit more in 1919, and they certainly responded as there were 1,200 exhibiting pork producers, 450 more than any other county fair in the state. Because of good weather, exhibits and entertainment, the four day attendance for the 1919 fair was estimated at 48,500.

It’s doubtful that the founding fathers of the Clay County Fair Association ever dreamed that they were establishing an institution that would involve the efforts, energy and ingenuity of not only Spencer, but the entire county. Yet in 1920, only the third year of the fair, the press was already calling it “Iowa’s Greatest County Fair.” It wasn’t until 1923, however, that this claim was officially printed on the premium book, and carried that boast through the 1928 fair.

It was after a “madly enthusiastic crowd” of 110,105 people enjoyed the fair of 1928 that the Clay County Fair became “The World’s Greatest County Fair.” All official references since that time have carried the slogan. Leo Dailey, secretary from 1927 to 1937, stated in 1932 that the slogan was taken when statistics proved the Clay County Fair to be the largest in the United States.

By 1931, it was felt that a new Grandstand was needed to replace the original, as there was not enough seating capacity to accommodate the thousands who daily flocked to see acts, stage shows, horse and car races. A new, all steel and concrete Grandstand was built at a cost of $45,000, which would seat 5,000 people comfortably. It was felt that the new Grandstand, still being used today, represented one of the most ambitious undertakings ever attempted by a county fair in the nation.

There were several other changes and additions to the fairgrounds over the years. In 1954, the Commercial Exhibits building was constructed at a cost of $174,498. The 208′ x 136′ building was built without pillar or support in the center in order to make the space adaptable for many uses throughout the year.  In 2003, the Clay County Regional Events Center was opened on the fairgrounds adding over 30,000 square feet of meeting and exhibit space.

Today the Clay County Fair is accepted not only as one of the largest county fairs in America, but has the added honor of being considered as one of the most rural-oriented fairs still in operation. The enlargement of the agribusiness/farm machinery display area to thirty-five acres made it the largest such display of any fair in the United States or Canada.  Altogether, there are more 2500 fairs operating in the US and Canada, and the Clay County Fair ranks in the top 100 in attendance annually.