The southernmost country in which rhino populations have roamed is South Africa.
Step-by-step explanation:
No Rhinos have ever existed in any country that falls south to South Africa on latitudes. This makes South Africa the southernmost country on the planet in which Rhinos exist and Rhino populations have roamed.
South Africa acts as a home to three distinct species of Rhinos. It is also known to host over 80% of the world's total Rhino population.