This year's outbreak is on pace to surpass last year's cases, when 118 people from 15 states and the District of Columbia were reported to have measles.
The cases in Florida's Gulf coast county of Pinellas are the first there in 10 years.
In 2014, the United States experienced a record number of measles cases, with 667 cases from 27 states reported to CDC's National Center for Immunization and Respiratory Diseases.
While vaccinations have kept measles to low levels in the US, it's still common in many parts of the world and the CDC says people who have it keep traveling to the U.S.
From Jan. 1 through July 14, there were 107 cases of measles reported in 21 states as well as the District of Columbia.
Now, doctors are urging parents to get their kids vaccinated with the measles, mumps and rubella (MMR) shot.
"We are continuing to investigate, but we would like families to know that their children could be exposed to diseases like measles anywhere and unless they're protected with vaccination they are risking potentially serious health effects for their child", Dr. Ulyee Choe, an infectious disease specialist and the county's health director, said in a statement Monday. Health officials said the residents had not been vaccinated and the visitor's vaccination status was unknown.
Measles is vaccine-preventable illness that's spread through a contagious person's sneezing and coughing. Some symptoms are a high fever, cough, runny nose and red eyes, followed by a rash that typically starts on the face and spreads to the rest of the body.