Off-duty sheriff's deputy Matt Dammerman said the walkers were instructed to proceed about an arm-length apart from one another.
"That will enable us to cover every inch of the field," Dammerman said.
After fanning out along a passageway between the two fields, searchers combed the south field in the early morning hours. By noon, the group was in the north field directly behind the Baptist church.
Dammerman said morale was good despite the daunting task of finding a second-grader less than four feet tall in what has become an 18-square mile search perimeter centered on the village of Watson. The village itself is about four square miles.
Willow had just started the second grade at South Side School in Effingham, authorities said.
That means most of the search area is rural terrain. While some of it is covered with maturing corn and beans, other parts of it are too rugged for even an all-terrain vehicle.
A group of horsemen were called in Monday to assist, including horseman Kevin Zerrusen of the Green Creek community north of Effingham.
"We can get to a lot of places that even four-wheelers can't," Zerrusen said. "We're up higher than the other searchers, and we can cover a lot of ground."
Chief Matt Kulesza of the Watson Fire Protection District said the search area included wide variations in terrain.
"We're looking at four square miles that is the village," Kulesza said. "The rest of it is rural, with some pretty steep hills and gullies."
Kulesza said the search area also includes some larger creeks that a girl Long's size would not be able to cross.
Acting Chief Deputy John Niccum of the Effingham County Sheriff's Department said there continues to be no evidence of foul play in connection with Long's disappearance. It is for that reason that authorities have declined to issue an Amber Alert.