There are two holidays celebrated in October in the United States: Columbus Day and Halloween. Columbus Day is on October 12, although it is celebrated on the second Monday of the month. Halloween is on October 31.
Columbus Day recognizes the anniversary of Christopher Columbus's arrival in America. It became a federal holiday in 1937, although it has been celebrated unofficially since the late 18th century.
Halloween is celebrated on the eve of the Christian holiday of All Hallows' Day. This was traditionally a day for remembering the dead. In the United States, it is typically celebrated by dressing up in costumes, telling scary stories and eating candy.