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 - a move that 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 will 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 30 prison employees, have already aided in sandbagging efforts throughout the state, according to a Department of Corrections spokeswoman.