The 20° S line of latitude passes through four South American countries:

1. Brazil: It runs across the northern part of the country, including parts of the Amazon rainforest.

2. Bolivia: It cuts across the central region of the country, passing through the city of Santa Cruz de la Sierra.

3. Paraguay: It runs through the southern part of the country, passing through the capital city of Asunción.

4. Argentina: It crosses the northern part of the country, passing through the provinces of Salta, Jujuy, and Formosa.