From the record
“The Pottawatomie County Fair Pavilion, at the Pottawatomie County fairgrounds in Onaga, Kansas, was built in 1921. It was listed on the National Register of Historic Places in 2004.”
Wikipedia article Pottawatomie County Fair Pavilion, CC BY-SA 4.0.
One of 14 National Register listings published here for Pottawatomie County · listed in 2004 · category: Building · built in 1921.
Sources: the Wikipedia article · the National Register database, National Park Service