The case involves a Thunder Bay-area resident, with the exposure category unknown.
There were three active cases across the district as of Thursday, and no district residents in hospital with the virus.
Only seven new cases have been reported in the Thunder Bay District over the past month, while the number of active cases has remained below five since June 30.
The health unit has reported a total of 3,346 confirmed COVID-19 cases since the pandemic began. Of those, 3,279 are considered resolved and 3 were active, while the virus was a contributing or underlying cause of 64 local deaths.
