SPRINGFIELD - As local emergency agencies continue battling floodwaters, state government officials consider how to offset the unforeseen costs of such extensive damage.

Gov. Rod Blagojevich declared Jersey and Winnebago counties disaster areas Monday, bringing the total number of counties affected by flooding to 17 since Wednesday.

The declaration came as the Mississippi River continued rising and the Rock River swelled from heavy rains and floodwater flowing in from Wisconsin.

So far, the state has laid down 2.8 million sandbags along riverbanks and has plans to lay down 4.5 million more, the governor's office said.

Patti Thompson, spokeswoman for the Illinois Emergency Management Agency said the state relies on a disaster relief fund to finance rescue and recovery efforts during disasters, but determining the total cost of damages is trickier with floods.

"If the water isn't all down, it can be hard to make sure that you're getting a full assessment of it," Thompson said. "The timing for any type of damage assessment is hard for me to predict."

Thompson said there is a possibility the state will seek a federal declaration of disaster. Such a move, if successful, would net federal reimbursement for three-quarters of costs related to flood response.

Getting the disaster declaration requires an assessment of damages. Thompson said for Illinois, about $15 million in damages would warrant federal aid but assessing the damages would need to wait until floodwaters recede.

"The first step is already in place, since we have the state disaster declaration in place," Thompson said."

In the past, the largest cost to the state has been the repair of damaged roads and bridges, but preparation and relief efforts also can have financial consequences. In 1993, the Illinois Department of Corrections helped by sending inmates to aid state workers.

In doing so, the department racked up 20,000 hours of unbudgeted staff overtime and about $1.2 million in flood-related costs that later caused some vacant positions within the department to remain temporarily unfilled to recoup the lost dollars.

This time around, more than 230 inmates, supervised by about 160 prison employees, have already aided in sandbagging efforts throughout the state, according to a Department of Corrections spokeswoman.

Drinking water was of particular concern in Quincy, where there is a water treatment plant. Though officials were confident Monday the plant was well protected from the swollen Mississippi, if floodwater reached the plant, "It could potentially take out the water supply for 40,000 people," said David Rudduck, a spokesman for Blagojevich.

If residents suddenly found themselves without water, the state has a stockpile of nearly 100,000 gallons that can be sent to communities that need it, according to the governor's office.

At one of four sites in Quincy alone, between 3,500 and 4,000 sandbags were being filled each hour, said Julie Shepard with the Adams County Emergency Management Agency. She said the Mississippi had reached 28.7 feet there Monday afternoon and was expected to crest at 31.9 feet.

Most of the sandbagging efforts were focused on the stretch of about roughly 300 miles from the Quad-Cities area south past Quincy and through Pike County, Thompson said.

As the water has climbed, it has threatened the approaches of bridges across the Mississippi. On Monday, the Illinois Department of Transportation was shoring up the Illinois approach of the only major bridge that links Hamilton to Keokuk in Iowa, using 16,000 tons of rock to elevate a 2,000-foot section of U.S. Highway 36.

Illinois has thus far not seen anywhere near the number of evacuations as communities across the river, particularly in Iowa. But the American Red Cross chapters have set up shelters across the state, including the Quad Cities area, Quincy and Rockford.

DISASTER AREAS

Gov. Rod Blagojevich has declared 17 counties state disaster areas because of recent flooding. They are Adams, Calhoun, Clark, Coles, Crawford, Cumberland, Douglas, Hancock, Henderson, Jasper, Jersey, Lake, Lawrence, Mercer, Pike, Rock Island and Winnebago.

Kenneth Lowe can be reached at kenneth.lowe@lee.net or 789-0865. The Associated Press contributed to this report.