The Illinois Department of Public Health made the announcement on Thursday and said the CDC confirmed the variant in a Rock Island resident.
"We expected to see more cases of variants detected in Illinois, including the B.1.351 strain," said IDPH Director Dr. Ngozi Ezike. "These variants seem to spread more rapidly, which can lead to more cases of COVID-19 and even another surge."
Cases of the B.1.351 variant were first reported in the U.S. at the end of January.
"Having this new variant in our community underscores the need to take personal precautions to prevent further spread. Please continue to wear your mask when away from home, watch your distance when around others and wash your hands frequently," said Rock Island County Health Department Administrator Nita Ludwig.
Officials say that Illinois is also currently reporting 22 cases of the B.1.1.7 variant, which was first identified in the United Kingdom.
So far, studies suggest that antibodies generated through the current COVID-19 vaccines recognize these variants and may offer some protection, officials say.
Viruses constantly change and new variants are expected. In addition to the B.1.1.7 and B.1.351 variants, the P.1 variant has emerged in Brazil.
Wearing a mask, staying at least 6 feet apart from others, avoiding crowds and washing hands frequently remain the best tools for preventing the spread of this virus, no matter the strain, health officials say.