Public Health Ontario says there are now 156 cases in Ontario, up from 133 on July 11 and 101 on July 6, with 124 of the total in Toronto.
The first female case was confirmed through diagnostic testing sometime in the past three days.
No other patient information was made available.
There are eight other possible cases in the province that remain under investigation.
Of those 156 cases, Public Health Ontario says 124 are in Toronto.
Ottawa has reported 11 cases, Middlesex-London has reported four and Halton Region has reported three cases.
The number of confirmed cases per day appears to have slowed significantly since late June, when public health units were detecting as many as nine cases a day.
The slowdown coincides with the start of a “ring strategy” to administer the smallpox vaccine to people most at risk of infection in the province.
Nine people have needed hospital admission for monkeypox in the province in the past two months and one person has needed ICU treatment.
While anyone can contract and transmit monkeypox, the recent outbreak in Europe and North America has seen significant spread among gay, bisexual, and men who have sex with men.
All confirmed cases in Ontario were in adults between the ages of 20 and 69.
Monkey pox is usually spread through prolonged close contact between people who breathe, talk, cough or sneeze.
It can also be spread through skin-to-skin contact with rashes or body fluids, and it can also remain on objects such as clothing or linens that have been in contact with an infected person.
Symptoms can appear anywhere between five to 21 days after exposure.
Federal guidelines indicate that the smallpox vaccine is most effective if given within four days of exposure to a case, but may help if given up to 14 days after exposure.
The City of Toronto continues to offer Imvamune smallpox vaccine to people considered to be at high risk of exposure.
There is also a treatment known as TPoxx which has been shown to be useful in cases where patients have suffered severe complications from infection.
The World Health Organization (WHO) now says it is aware of 6,027 laboratory-confirmed cases of monkeypox in 59 countries worldwide, including three deaths.
The Public Health Agency of Canada (PHAC) says it knows of 477 cases across Canada, with the most in Ontario and Quebec.