Option 1: South Africa is not located at the southernmost latitude. South Africa is situated in the southernmost part of the African continent, but it does not extend as far south as some other countries.

Option 2: Australia is also not located at the southernmost latitude. While Australia does have some regions that are located in the southern hemisphere, it is not the southernmost country in terms of latitude.

Option 3: Chile is the correct answer. Chile is a country located in South America and it extends quite far south, reaching a latitude of about 56 degrees south. This makes it the country with the most southern latitude out of the options provided.

Option 4: Polynesia is not a specific country or location, but rather a region in the Pacific Ocean that encompasses a group of islands. As such, it is not possible to determine a specific latitude for Polynesia.

Therefore, the correct answer is option 3: Chile.