Health officials in the county described that figure as "extremely high."
The Warren County health department said on Wednesday: "Not only is this above the county average, it also meets the Ohio Department of Health definition of an outbreak."
And in western Massachusetts, doctors are seeing "a whole lot" of walking pneumonia cases, which is a milder form of the lung condition.
Experts said that neither of the outbreaks in Massachusetts and Ohio is being caused by a novel pathogen - instead, it is a mixture of seasonal bacteria and viral bugs hitting at once.
Fears of the spreading infection are rising in the US as hospitalizations rapidly increase in China and other European countries.
While the Centers for Disease Control and Prevention (CDC) said that "nothing is out of the ordinary," there is an "ongoing investigation" underway in Ohio into what is triggering the wave of illness.
Patients in Warren County - which is home to almost 250,000 people - have tested positive for mycoplasma pneumoniae, strep, and adenovirus.
The average age of patients is eight, but some are as young as three. Most patients are suffering from a fever, cough, and fatigue, doctors said.
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Medical experts said the main issue in Massachusetts is RSV, a respiratory virus that kills more than 100,000 Americans each year.
Dr. John Kelly from Redwood Pediatrics in East Longmeadow told Western Mass News: "This is the season for RSV and we're seeing a whole lot of it...a lot of kids with upper viral respiratory infections, cough, runny nose, some fevers and the thinking with RSV is that it can cause lower viral respiratory infections, so they get spread to your lungs."
There are several theories as to what caused the outbreak, including that children's immunity has been weakened by lockdowns and mask-wearing during the Covid pandemic, leaving them more vulnerable to illness.
Warren County Health District officials said in a press release: "We do not think this is a novel/new respiratory disease, but rather a large uptick in the number of pneumonia cases normally seen at one time.
"As we approach the holiday season, when many of us will be gathering together with family and friends, please remember to take necessary precautions to protect your health."