Fifteen families took that first step Monday, informing officials they plan to sue over the outbreak at last summer's Lane County Fair.
Nine other families may also take legal action, their lawyer said.
In all, 82 fairgoers were infected with E. coli, the biggest such outbreak in state history. Nearly two-thirds of those were children under age 6.
Twelve children were sent to Portland hospitals for treatment of hemolytic uremic syndrome, a potentially fatal complication of E. coli infection that causes kidney failure.
Seattle lawyer Bill Marler notified county and fair board officials that he would file outbreak-related claims on behalf of the families. Such notice is required under state law.
Once claims are filed, likely within 30 days, county attorneys will review them and decide whether to pay the families. If the county rejects the claims, the families can file suit.
"The fact the outbreak happened is evidence the fair did not do enough to protect kids from becoming ill," Marler said.
The 15 families represent 14 children and four adults. Among those filing were Bill and Shelly Walter, whose 2-year-old daughter, Carson, spent 31 days at Doernbecher Children's Hospital in Portland, including two stints in the pediatric intensive care unit. She underwent 17 rounds of dialysis that filtered toxins from her blood.
Bill Walter said he hopes a lawsuit will force the fair to reduce the E. coli risk for people attending future fairs and he hopes a jury award or settlement will ensure his daughter gets the future medical care she'll likely need.
Oregon's "tort caps" law limits the liability of government agencies. Under the law, the most any single family could recover from the fair board is $200,000.
E. coli is most commonly spread through contaminated ground beef and water. But public health investigators traced the fair outbreak to the sheep and goat exposition hall on the south side of the fairgrounds.
At next summer's fair, officials said they plan to increase the number of hand-washing stations, educate the public about how to behave around animals, use greater vigilance to keep animal areas clean and install hygienic mats for wiping shoes outside animals barns.
Warren Wong, managing director of the fair, said he doesn't think the fair board will be held responsible for the outbreak.
"Our insurance adjusters and attorneys have opined that the fair did not do anything that was negligent, so we don't believe that we are liable," he said.