There's information at Farnsworthhouse.org and at the National Trust site.
The house, which is near the Fox River in Plano, Illinois, has flooded before, most recently in 1996, an event that the National Trust says caused hundreds of thousands of dollars of damage and took months to repair. This year, the Trust reports:
The Farnsworth House, fell prey to Mother Nature Saturday, September 13, and Sunday, September 14, as more than eight inches of rain fell in two days from Tropical Storm Lowell, immediately followed by the remnants of Hurricane Ike. Fox River waters rose two feet over the top deck, entering the Farnsworth House interior. Built within the flood plain of the Fox River in Plano, Illinois, the house is supported by columns more than five feet above the ground which proved not high enough as record breaking rain amounts brought the river more than fourteen feet above its normal level. -- ta