NWS meteorologists conducted a ground survey Friday of the most heavily damaged areas. Early findings indicate that the tornado tracked from near Rochelle to near Belvidere, including Fairdale, in a single track, NWS said.
So far, at least two other tornadoes - an EF-0 in Cherry Valley and an EF-1 near Belvidere - have also been discovered by NWS surveyors.
PHOTOS: Tornado damage, the day after
NWS says it will conduct an aerial survey in the next day or two to confirm the final rating and if any other tornadoes were present.
As crews surveyed the damage and spoke to residents, many said the advance warning from sirens, television and social media was crucial.
"I believe it was 27 minutes between the time we issued the notification through the sirens that the first funnel cloud was sighted," said Ogle County Sheriff Brian VanVickle.
BIRDS-EYE VIEW OF DEVASTATION
On Friday, ABC7 got a bird's eye view of the tornado's path of devastation from Chopper 7HD. Fairdale was hardest hit, where officials said every home in the town was damaged, and 17 were completely destroyed.
About 15 Illinois agencies were part of the tornado response team overnight. With daybreak on Friday, officials could finally see how vast the damage was.
Three miles southwest, the tornado damaged a few homes in Monroe Center and carved swirls into farm fields as it charged into Fairdale.
Near Belvidere, cows are corralled by debris after a section of the barn's roof broke free and collapsed. At Summer Field Zoo, a few animals and buildings were lost, but the surviving reindeer, horses and wolves were visible outside.
From the air, it's easy to see what a different story this would be had the tornado tracked just a quarter mile north or south. Then, only fields would have been destroyed.
VIDEO: Decoding 'X-codes' used by search-and-rescue teams