The OAS was founded on May 5th, 1948 with these 21 charter members:
Argentina
Bolivia
Brazil
Chile
Colombia
Costa Rica
Cuba
Dominican Republic
Ecuador
El Salvador
Guatemala
Haiti
Honduras
Mexico
Nicaragua
Panama
Paraguay
Peru
United States
Uruguay
Venezuela
The following countries joined the Organization of American States (OAS) after the initial creation. The date following the country name is the year that they joined: