The man, who is in his 20s, had recently traveled to Wuhan, China, and sought medical care soon after returning home, according to a statement from the Massachusetts Department of Public Health.
Massachusetts Public Health Commissioner Monica Bharel said the man was recovering and was grateful that he sought medical attention immediately.
She said that while the state has been preparing for a possible case, the risk to the public "remains low in Massachusetts."
Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, emphasized at a press briefing Friday that the risk to the general American public is low.
"We want to keep it at a low risk," he said.
The eight cases in the U.S. include seven in travelers and one human-to-human transmission between a husband and wife. The affected states are California, Illinois, Massachusetts, Washington state and Arizona. In China, there have been 11,821 confirmed cases as of Saturday and 259 people have died. Outside of China, 170 cases have been confirmed in 25 countries.
The new case in the U.S. comes a day after Secretary of Health and Human Services Alex Azar declared a public health emergency in the country at a White House press briefing on coronavirus.
U.S. citizens returning from Hubei province in the previous 14 days will be subject to up to a 14-day quarantine. Foreign nationals, other than immediate family members of U.S. citizens who have traveled to China in the previous 14 days, will be denied entry into the country. The temporary measures take effect Feb. 2 at 5 p.m.
Americans who've traveled to other parts of China in the previous 14 days will be subject to a health screening upon entry and asked to self-quarantine for up to 14 days.
The Centers for Disease Control and Prevention ordered a federal quarantine order for all 195 people who were evacuated from China and have been voluntarily quarantined at a military base in California.
Americans should not let panic or fear guide their actions, according to the CDC, who recommended that the general public does not need to wear face masks.
Many questions remain about how the virus is transmitted and how infectious it is, with countries scrambling to react.