Why it starts on September 15

“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 September18, respectively.”

The Census Bureau puts it the same way: “The designated period is also a nod to those from Mexico and Chile, which celebrate their independence September 16 and September 18, respectively.” (Census Bureau, Facts for Features 2026)

The 31 days in 2027

Our calculationWeekdays for 2027. The marked independence days and October 12 are the dates the Library of Congress portal names; the federal Columbus Day holiday is the second Monday in October under 5 U.S.C. § 6103.

• September 15: independence anniversary of Costa Rica, El Salvador, Guatemala, Honduras and Nicaragua. September 16: Mexico. September 18: Chile.
• October 12: the date the portal gives for Columbus Day or Día de la Raza.
• Monday, October 11, 2027: Columbus Day as a federal legal public holiday (second Monday in October).

Who the month honors

“National Hispanic Heritage Month celebrates the contributions of Americans tracing their roots to Spain, Mexico, Central America, South America and the Spanish-speaking nations of the Caribbean.”

“The Library of Congress, National Archives and Records Administration, National Endowment for the Humanities, National Gallery of Art, National Park Service, Smithsonian Institution and United States Holocaust Memorial Museum join in paying tribute to the generations of Hispanic Americans who have positively influenced and enriched our nation and society.”

A week first, then a month

“The observation started in 1968 as Hispanic Heritage Week under President Lyndon Johnson and was expanded by President Ronald Reagan in 1988 to cover a 30-day period starting on September 15 and ending on October 15.” (hispanicheritagemonth.gov (Library of Congress))

Public Law 100-402 itself says a “31-day period beginning September 15 and ending on October 15”. Counting both end dates gives 31: 16 days in September and 15 in October.

“In 1968, Congress set aside a week for this observance and two decades later expanded it to a month stretching from September 15 to October 15.” (Census Bureau, Facts for Features 2026) The proclamations page has the text of both laws.

Questions

Which countries have independence days during the month?

“The timing is historically significant as September 15 is the anniversary of independence in Costa Rica, El Salvador, Guatemala, Honduras and Nicaragua.” (Census Bureau, Facts for Features 2026) “In addition, Mexico and Chile celebrate their independence days on September 16 and September18, respectively.” (hispanicheritagemonth.gov (Library of Congress))

Is October 12 part of it?

The date falls inside the period. The Library of Congress portal says: “Also, Columbus Day or Día de la Raza, which is October 12, falls within this 30 day period.” (hispanicheritagemonth.gov (Library of Congress))

That sentence gives the anniversary date. The federal holiday follows a different rule: “Columbus Day, the second Monday in October.” (5 U.S.C. § 6103 (govinfo))

Our calculationIn 2026 the second Monday in October was October 12; in 2027 it is October 11. On the 30 days the portal mentions: Public Law 100-402 itself says a “31-day period beginning September 15 and ending on October 15”. Counting both end dates gives 31: 16 days in September and 15 in October.