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- October 3, 1776 - The Municipality of Vega Baja was founded.
- October 5, 1893 - Banco Popular was established.
- October 11, 1918 - A 7.3 (Richter scale) earthquake occurred off the west coast of Puerto Rico, accompanied by a 6.1 m (20 ft) tsunami.
- October 13, 1981 - Birth of Ángel Figueroa, professional basketball player
- October 14, 1952 - Birth of Rick Aviles, comedian and actor (d. 1995)
- October 15, 1938 - Birth of Antonio R. Barceló, first PR Senate President and grandfather of Governor Carlos Romero Barceló (d. 1868)
- October 18, 1733 - The Municipality of Añasco was founded.
- October 21, 2003 - Death of Luis A. Ferré, third Governor of Puerto Rico (b. 1904)
- October 22, 1928 - Fi Sigma Alfa fraternity is established at the University of Puerto Rico, Río Piedras Campus
- October 22, 1979 - Birth of Kermit Cintrón, professional boxer
- October 23, 1939 - Death of Antonio S. Pedreira, renowned author and educator (b. 1899)
- October 24, 1935 - The Río Piedras massacre occurred.
- October 24, 1994 - Death of Raúl Juliá, Golden Globe award winning screen and stage actor (b. 1940)
- October 25, 1852 - The Municipality of Santa Isabel was founded.
- October 27, 1880 - The Municipality of Culebra was founded.
- October 29, 1908 - Birth of Jaime Benítez, author, academic, politician (d. 2001)
- October 29, 1980 - Birth of Miguel Cotto, welterweight boxing champion
- October 30, 1950 - The Jayuya Uprising occurred.
- October 31, 1960 - Birth of Luis Fortuño, tenth Governor of Puerto Rico
October