West Nile Virus is carried by mosquitoes and transmitted through a bite by an infected insect.
The Wisconsin Division of Public Health will continue surveillance for West Nile virus until the end of the mosquito season.
At least two of the other nine human cases involved Flower Mound residents.
There have been 20 horses diagnosed in the state so far in 2017.
"Detection in chickens means there is a risk of potential spread to humans via mosquitoes", Santa Barbara County Public Health Officer Dr. Charity Dean said in a statement.
Vaccinations are available for horses from area veterinarians.
Remove all sources of standing water around your home and yard to prevent mosquito breeding. "When cold weather arrives, the mosquitoes will be eliminated, but until then, people are urged to take measures to protect themselves".
West Nile virus is passed primarily between birds by mosquito vectors.
The new cases are in Hinds, Rankin, and Sunflower counties.
Meanwhile, no instances of the Zika virus infection have been reported in the county.
No Jefferson County residents have been reported ill in the past two years. Human-to-human transmission does not occur.
The majority of people, 80 percent, who are infected with West Nile Virus do not get sick. Some will have very mild symptoms such as fever, headache, and body aches which subside after a few days to weeks.
Most people with these symptoms recover completely. There are no vaccines to prevent or medications to treat the virus, and about 1 out of 150 infected people develop a serious, sometimes fatal, illness, according to the Centers for Disease Control and Prevention.