JEFFERSON COUNTY, Mo. — A "female between 10-20 years of age" tested positive for COVID-19, the Jefferson County Health Department confirmed Tuesday evening. It is the county's fourth case.

Jefferson County reported its first three cases Monday afternoon. Those cases were announced just hours after the county was placed under a stay-at-home order.

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The latest case in Jefferson County is one of eight patients in Missouri under the age of 20. St. Louis County has one patient under the age of 10 and three between the ages of 10 and 19, data provided by the county said Tuesday.

Illinois has reported a coronavirus case in a patient under the age of 1.

There are 270 confirmed cases of COVID-19 in Missouri. As of Tuesday evening, St. Louis County has 100 cases, St. Louis has 37 and St. Charles County has 11. All three have one death.

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Local and state leaders said they expect the numbers to increase as testing capabilities increase. 

The state also made changes to testing requirements Monday that could allow more people to get tested.

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