Grundy County was first organized in 1856. The county seat is Grundy Center. In 1857 a building for county business was built and it was known as the "Old Cheese Box". It was the only county courthouse in the state of Iowa that was octagonal in shape. This eight-sided building served the county for forty years until the second and present courthouse was finished in 1891.
This imposing stone castle was constructed for $45,532.48. The contractor used the best materials and workmanship so that even today, the courthouse is in nearly its original state.