January – February – March – April – May – June – July – August – September – October – November – December
- August 2, 1797 - The Municipality of Juncos was founded.
- August 4, 1909 - Birth of Manuel Méndez Ballester, journalist, radio and television broadcaster, and teacher (d. 2002)
- August 5, 1898 - American troops arrive and capture the town of Guayama, an event known as the Battle of Guayama.
- August 8, 1508 - The first settlement on the island, Caparra, is established by Juan Ponce de León.
- August 8, 1511 - Pope Julius II established the first Roman Catholic diocese in Puerto Rico, one of the first three in the entire New World.
- August 9, 1898 - The town of Coamo is besieged and subsequently seized by American troops in the Battle of Coamo.
- August 9, 1898 - American troops face small remnants of Spain's 6th Provisional Battalion at the Guamani River, an event known as the Battle of Guamani.
- August 10, 1815 - The Royal Decree of Grace was issued, allowing foreigners to enter Puerto Rico and opening the port to trade with nations other than Spain.
- August 10, 1898 - American troops face Spanish soldiers in Hormigueros in the Battle of Silva Heights.
- August 10, 1966 - Birth of Juan Rivera, professional wrestler
- August 11, 1815 - The Municipality of Adjuntas was founded.
- August 11, 1903 - Death of Eugenio María de Hostos, educator and independence advocate (b. 1839)
- August 12, 1898 - The Battle of Aibonito Pass, the last battle of the Puerto Rican Campaign of the Spanish–American War, occurred.
- August 17, 1773 - The Municipality of Cayey was founded.
- August 18, 1934 - Birth of Roberto Clemente, Major League Baseball player and first Hispanic American to be selected to the Hall of Fame (d. 1972)
- August 25, 1928 - Birth of Miguel Ángel Álvarez, also known as "El Men", comedian and actor.
- August 27, 1974 - Birth of José Vidro, Mayor League Baseball designated hitter
- August 28, 1957 - Birth of Luis Guzmán, actor