There's already been flooding in many parts along the river.
On Monday afternoon, officials met to discuss what will happen next in their communities.
Water levels through the Fox Chain of Lakes and its tributaries continued to rise and are expected to rise more through the end of the week. Residents say they are afraid and concerned.
The residents have been through three major flood storms since August. Jeff Costanza has lived in the area for 45 years.
"This is way worse than any flood we've had since the '70's. I have never seen it this bad. What I understand, it is going to get a lot worse. It is not done yet," he said.
Many are getting involved with helping each other, including the Freeman family, filling sandbags.
"My house is out of the water. We're helping a neighbor down the street who is older and the water is up to the top of his sandbag wall. We are just helping him stay dry," said David Freeman.
Flood levels around the Fox Chain of Lakes and the Lower Fox River are expected to rise 2 - 3 inches potentially over the next several days with the crest predicted at the end of the week. The state is stepping up flood containment and relief efforts at several locations.
"The Fox River upstream from the chain of lakes, this is the part of the river that flows through the Fox River Spring subdivision through the Antioch township. This section of the river appears to have crested today at levels several inches over what we saw in August. We're working with the Red Cross, Salvation Army and other agencies to begin to offer assistance to residents who have been impacted," said Kent McKenzie, Lake County Emergency Management.
"This is a dangerous situation. As much as we want to get the news out to everybody, we want the general public to please stay out of these areas," said Steve Smouse, Antioch Township supervisor.
The Illinois Department of Resources has designated the Fox River from the Wisconsin border to the Algonquin area, including the chain of lakes, as a restricted boating area.
"That action is only enacted when there are serious threats to navigation, in this case, on the river parts because of high currents and throws and on the lakes because of extensive debris," said McKenzie.
A little before 10 a.m. Monday, a boat capsized. Three men were pulled out of the water. One was pronounced dead. It's still unknown why they were in the water.
Furious sandbagging efforts continued on the state's northeast side, where the Fox River -- expected to crest over the next week or so as waters roll down from Wisconsin -- seeped into the village of Antioch and crept ever-closer to businesses and homes along main routes and subdivisions.
"It's going to be a matter of putting sandbags up and holding back...I do not see where evacuations are going to be an issue," said Lee Shannon, the far-northern Illinois community's emergency management chief. "Though there's a plan in place if need be."
At Sequoit Harbor Marina on Lake Marie in Antioch, general manager Doug Kolian estimated 1,000 sandbags were stacked along the building's outer walls to protect the boats and other merchandise inside.
"We've got five pumps going behind the sandbags, keeping the water from seeping into the showroom," Kolian said. "Right now, if it goes up a little, we should be OK...if it goes up another foot or more though, we could be in trouble."
While waterfront residents tried to keep floods at bay, a band of ferocious storms packing 65-mph gusts moved across northern Illinois.
ComEd spokesman Luis Diaz said as many 140,000 customers lost power -- the fifth time storms have left communities in the dark in the past ten days.
"The damage was widespread in our service territory and in some cases rather severe," Diaz said. "We had downed power lines, broken poles, lightning damage."
National Weather Service meteorologist Stephen Rodriguez in Chicago noted another round of storms was expected to continue its move across the Midwest and pelt the soggy state later Sunday.
"It's a very active weather pattern able to produce a good amount of rainfall," he said.
Elsewhere in Illinois"We're just biding the raising of the water and helping people who have to get their stuff out," said George Askew, an alderman in downstate Keithsburg, where multiple levee breaks prompted voluntary weekend evacuations.
Askew said water sat as high as 3 or 4 feet in some parts of the small Mississippi River community of 700 residents, about 35 miles southwest of Moline. The National Weather Service said the river was expected to crest there Tuesday just above 25 feet. Flood stage in the area is 14 feet.
"A lot of basements are full of water, another foot will put it up into some of their homes," Askew said.
The 76-year-old spent most of Sunday moving residents and as many belongings as possible to relatives' homes or campers on higher ground.
"We'd back down the pickup trucks as far as we could, then wade through 2, 3 feet of water to get the stuff they want to take out of their house," Askew said. "We've got the biggest share of the people out of the so-called (worst) flooded areas."
While 15 counties remained designated state disaster areas, authorities said no deaths have been reported in connection with Illinois' floods as of Sunday.
Not far north of Keithsburg, the Quad Cities Area American Red Cross balanced emergency response and preparation in two states. The group set up six area shelters, three of them on the Illinois side of the Mississippi, and put volunteers on high alert while distributing clean-up kits and financial assistance.
"Right now, Iowa is probably going to be more affected by the flooding, but we are operating on both sides of the river," said spokeswoman Leslie Anthony. "I think it's probably going to get a lot worse over the next couple of days and that's when we'll really beef up our presence."
Also along the Mississippi, more than 400 members of the Illinois Army National Guard were activated to assist with sandbagging efforts in Quincy. There, the river is expected to crest midweek and the two-lane Memorial Bridge already has been closed. The Champ Clark Bridge about 50 miles south along the river also was closed.
"We're trying to be prepared," said Illinois Emergency Management Agency spokeswoman Patti Thompson.
The Adams County Chapter of the American Red Cross opened a shelter on Quincy University's campus Sunday afternoon capable of housing about 72 people.
River levels continued their ascent in the Rockford area, where the Red Cross reported at least 23 people took refuge in a shelter during the weekend.
It took a boat to get Kedric Hawthorne and his family from their Rockford home along the shore of the Rock River, which is expected to crest about 5 feet above its flood stage sometime Tuesday.
"I feel homeless," he told the Rockford Register Star for a Sunday story.
In southern Illinois along the Indiana border, Lawrence County authorities continued to monitor levees along the Wabash River but reported no new breaches Sunday. Levee breaks earlier in the week had flooded a campsite near Lawrenceville and forced the evacuations of roughly 200 homes.
Just south, Wabash County Sheriff Joe Keeling expressed sympathy for what his Lawrence County counterparts and others have dealt with in the past week, and said relief sandbagging efforts in Mt. Carmel appeared to have been only precautionary.
"Our stretch of levees have been holding really well," he said.
The Associated Press contributed to this report.