National Hispanic Heritage Month is observed from September 15 to October 15 by celebrating the histories, cultures and contributions of American citizens whose ancestors came from Spain, Mexico, the Caribbean and Central and South America.
The day of September 15 is significant because it is the anniversary of independence for Latin American countries Costa Rica, El Salvador, Guatemala, Honduras and Nicaragua. In addition, Mexico and Chile celebrate their independence days on September 16 and September 18, respectively. Also, Columbus Day or Día de la Raza, which is October 12, falls within this 30 day period.
Source: Hispanic Heritage Month Site