Both South Dakota and Kansas in 2010 have spawned hailstones with diameters that smashed the previous record set in 2003 by Nebraska of 7 inches.
8 inch hailstone is the new record hailstone diameter
http://www.accuweather.com/blogs/weathermatrix/story/34506/was-largest-hail-stone-record-broken-friday.asp
Kansas hailstone with a diamter of 7.75inches which fell on September 15 2010 was not far from this record and also surpassed the previous record.
http://articles.kwch.com/2010-10-01/hail_24081951