You learn something new everyday. All I wanted to write tonight was that I spotted this octagon house in Monroe, on the way from Pella to Newton. Then I had to go and start wondering about the interior layout of such a house.
Octagon houses were an architectural fad that followed the publication of Orson Squire Fowler's 1848 opus, The Octagon House: A Home For All. Fowler was the leading proponent of phrenology, the science that the shape and bumps of your skull influenced your personality, in the mid 19th century.
Branching dangerously away from his expertise in boneheadedness, Fowler came to believe that octagonal houses would be much more cost effective than houses with those pesky right angles. Eight-sided houses should also let in more light and air. Fowler's design sense apparently only included the exteriors of the houses. In the real world it is difficult to fit functional rooms to spaces containing odd angles, so you get closets with windows and kitchens with lots of severe corners where dirt can gather.
A couple thousand octagon houses were built during the 1850s and 1860s, mostly in New York and Massachusetts. This amazing inventory says there are 404 octagon houses still standing. The house in Monroe is believed to have been built in the late 1860s.