Round Barns, which include truly round and many sided, can be found in many parts of the USA. The largest concentrations of this style of barn are found in the midwest (Indiana, Illinois and Wisconsin). Vernon county here in Wisconsin boasts more round barns than any other county in the USA. This claim is up for debate because Fulton county in Indiana makes the same claim and the town of Rochester, IN in Fulton county hosts a Round Barn Festival every year. Some of these unique barns are being preserved and taken care of while others are deteriorating and falling apart. One of the barns pictured below no longer exists.
Most round barns are built with a silo in the center of the barn. The round shape was supposed to make work in the barn, i.e. feeding or milking cows, more efficient. Another possibility for their construction: the round shape provided no corners for evil spirits to hide in.

Are you interested in learning more about barns in the United States? You might also be interested in these links:

The Barn Journal's Round Barns
Round Barns in Iowa (Maxheim Gallery)
Round Barn - Harney County, Oregon
Old Round Barn - Arcadia, Oklahoma
Inn at the Round Barn Farm
Fromme-Birney "Round" Barn
Old Barns (has one Round Barn photo)
Wisconsin Barns: Stories in Wood & Stone
Wisconsin Barn Preservation Program
Slayton Farms Round Barn
Round Barn Lodge and Restaurant
Round Barns (very large collection)
Round Barns of the Hillsboro Area
Round & Polybonal Barns (another large collection)
Amish Acres Round Barn
Sketches of Nebraska Barns

Round Barn photos and info submitted by other Round Barn enthusiasts.

The following is a list of directions to all of the round barns I have photographed or know of in Wisconsin:

Pierce County (Thanks to Barb Lewis)
1. On Hwy 65 between Beldenville and Ellsworth, take County J to the North 1.5 miles. Go east on 690th Avenue, 3/4 mile on left
2. Pierce County Fairgrounds in Ellsworth
3. Off Hwy 10 going towards Prescott, South on County Road OO

Washburn County
1. On County O south of Hwy 70 and west of Spooner

Barron County
1. On County P south of Cumberland
2. On the first road to the right south of Comstock. The barn is on your left just past Crystal Lake

Rusk County
1. On Hwy 27

Buffalo County
1. On County HH south of Hwy 10 east of Mondovi

Waupaca County
1. On Hwy 54 east of Hwy 22 before New London

Wood County
1. On County S 2 miles off of Hwy 10 near Milladore

Monroe County
1. On Hwy's 131 and 71 just east of Wilton
2. On County T north of County F and south of Norwalk
3. On Hwy 71 norhtwest of Norwalk

Vernon County
1. On County D north of County P
2. On a town road just outside of Dell
3. On a town road off of Hwy 131 south of Ontario

Columbia County
1. On County Z east of Hwy 146 and north of Fall River

Sauk County
1. On County N west of Hwy 23 and north of Plain

Sheboygan County
1. On County J 3 miles west of County M not far from Hwy 57

Dane County
1. On Hwy's 12 and 18 west of Cambridge