They cautioned that the investigation was still in the early stages and they have no indication the fair was the source.
They said the investigation could take days or weeks to complete.
Seven of the victims are from Wake County. The eighth is from Johnston County, and the ninth from Cleveland Co. The ninth case was not reported to Wake County. Local health officials said the state was investigating that case.
Most are children, but the ages range from 2 months to 62 years old.
Three are currently hospitalized in intensive care. Health officials said those three are children.
The State Fair is managed by the NC Department of Agriculture. Agriculture Commissioner Steve Troxler said his thoughts and prayers are with the patients and their families and he hopes for quick recoveries.
"We will provide any assistance necessary to help public health officials find the cause of this outbreak. At this time, there is still very little information about the potential source. We hope that as the science plays out, investigators will find answers," he said in a statement.
Health officials say although a cluster of E. coli cases is not uncommon, they need to know if there are additional cases.
"If someone does exhibit the symptoms, which [include] severe stomach cramps, diarrhea, those types of symptoms, fever, they do need to seek out medical help," said Sue Lynn, Wake County Human Services.
E. coli exposure often comes from contaminated water or food and is most likely found in raw vegetables and under cooked beef.
Signs of illness usually begin three or four days after being exposed to the bacteria, but some people may become sick as soon as one day after exposure.
Symptoms include diarrhea, abdominal cramping, pain or tenderness and nausea and vomiting.
For more information about E. coli, visit http://epi.publichealth.nc.gov/gcdc/ecoli.html.