A bell rung before an uprising, not at a proclamation ceremony
Miguel Hidalgo y Costilla was the parish priest of the small town of Dolores, in what is now Guanajuato state, and for months he had been part of a group quietly plotting an uprising against Spanish colonial rule. Spanish authorities found out. Rather than wait to be arrested, Hidalgo acted that same morning, summoning his parishioners with the church bell and speaking from the pulpit. Britannica and the Library of Congress both place the bell-ringing in the early hours of September 16, 1810, close to 2:30 a.m. No recording or transcript of what Hidalgo actually said survives, and the versions historians quote today, calling for an end to Spanish rule and invoking the Virgin of Guadalupe, are later reconstructions rather than a verbatim record.
The speech became known as the Grito de Dolores, the Cry of Dolores, and it marks the opening of the Mexican War of Independence, not the moment Mexico actually gained it. Hidalgo's own uprising didn't last long. Spanish forces defeated his poorly armed followers within a year, captured him, and executed him by firing squad on July 30, 1811. The war he had started kept going under other commanders for another decade.
Eleven years between the cry and the country
The fighting that followed Hidalgo's death dragged on under a rotating cast of insurgent leaders, most notably José María Morelos, until command eventually passed to Agustín de Iturbide, a royalist officer who switched sides in 1821 and issued the Plan de Iguala. Iturbide's forces, the Army of the Three Guarantees, had taken most of the country by the time Spain's newly arrived captain-general, Juan O'Donojú, met him at the town of Córdoba. The two signed the Treaty of Córdoba on August 24, 1821, recognizing Mexican sovereignty and setting terms for the withdrawal of the remaining Spanish troops.
The Army of the Three Guarantees entered Mexico City on September 27, 1821, and Iturbide proclaimed the independence of the Mexican Empire the following day. Even that wasn't quite the end of the story: the Spanish government in Madrid refused to ratify the Treaty of Córdoba and didn't formally recognize Mexico as a sovereign nation until the Santa María-Calatrava Treaty, signed December 28, 1836, a full quarter-century after Hidalgo rang his bell.
Why the party starts the night before
The loudest part of the holiday happens the evening before the date it marks. Each year on the night of September 15, the president of Mexico steps onto the balcony of the National Palace, rings a bell, calls out the names of the independence movement's most celebrated figures, and closes by shouting "¡Viva México!" three times. Towns and cities across the country repeat a smaller version of the same ceremony in their own main squares.
The bell the president rings isn't a replica. It's the actual bell from Hidalgo's parish church in Dolores, moved to the National Palace by President Porfirio Díaz and mounted in a niche above the balcony, where it stays year-round except for that one night. September 16 itself is the quieter of the two days by comparison, marked mainly by a military parade through Mexico City's Zócalo, a tradition dating back to the late 19th century.
Not Cinco de Mayo
Mexican Independence Day gets confused, mostly by people outside Mexico, with Cinco de Mayo, and the two mark entirely different events 52 years apart. Cinco de Mayo, May 5, commemorates a single battle, the Mexican army's 1862 victory over French forces at Puebla; within Mexico it's a modest regional observance, celebrated with real weight mainly in Puebla state itself. Its outsized profile in the United States came later, pushed by Mexican-American activists in the 1960s who connected the battle to their own civil rights movement, then promoted from the 1980s on by beverage companies marketing it as a drinking holiday.
September 16, by contrast, is Mexico's actual independence anniversary, the one that closes schools, banks, and government offices for the day. A search that turns up a date in May for "Mexican Independence Day" has found Cinco de Mayo's marketing footprint, not the holiday itself.
One date, inside a longer regional window
September 16 doesn't stand alone on the calendar. It falls on day two of National Hispanic Heritage Month, the federally designated U.S. observance that runs September 15 through October 15 specifically because that window brackets a cluster of Latin American independence days: five Central American countries share September 15 itself, Mexico follows on the 16th, and Chile's own independence day lands on the 18th.
That overlap means September 16 shows up in two different contexts depending on which country's calendar a reader is checking. In Mexico, it's a national legal holiday tied to the country's own founding. In the United States, it's one day inside a monthlong federal observance recognizing Hispanic and Latino heritage broadly, not a U.S. public holiday in its own right; U.S. federal offices stay open.