For 16 years the Mercer County Fair was held in Millersburg, Ill., on the southwest corner of the village. Beginning with the first Fair in 1853, they were held in October, harvest time. Buildings were erected on the three-acre site and an additional two acres were purchased later. No Fair was held in 1862 because of the Civil War. Mrs. Eliza Greer attended one of the Millersburg Fairs and saw ice cream for the first time. She wondered why people were eating mash potatoes in that way.
In 1869 the Mercer County Fair moved to Aledo. Aledo had become the county seat and the newly constructed railroad passed through the town bypassing Millersburg. Twenty-seven acres were purchased on the southwest corner of town for $100 an acre.
All the original buildings built on the new Fairgrounds have been destroyed. The small octagon Pumpkin House was erected in 1880 at a cost of $169.50. The much larger Floral Hall was built two years later at a cost of $2,020. Two brick buildings, the secretary’s office, and the ticket booth were built in 1914 and 1919. The Merchants Building was erected in 34 days in 1926. Because of financial difficulties, no Fair was held in 1938.The Fairgrounds were listed on the National Register of Historic Places in 1997.
The Sesquicentennial Fair was held in 2003.