Osa is a canton in the Puntarenas province of Costa Rica. The head city is in Puerto Cortés district. Osa was created on 29 July 1940 by decre…Osa is a canton in the Puntarenas province of Costa Rica. The head city is in Puerto Cortés district. Osa was created on 29 July 1940 by decree 185. In pre-Columbian times was populated by Boruca which left legacies such as fields and stone walkways.