In the 1860 census there is a George Johnson living in Crabapple, Iroquois co. Ill.(which is just a county away, to the south of Thorton) He is listed as 14 years old and birth place unknown. Maybe this is why you can't find a George Johnson turning up in the 1860 Illinois census as being born in Norway? He was living with Simpson and Phebe Gallsmore?/Gillmore? Also, Thorton was very close to the Indiana border. You may want to check in Indiana for your George Johnson.