It is Memorial Day Holiday in the US.
Here are all national holidays in Japan in 2018.
January 1 New Year's Day
January 8 (second Monday of January) Coming of Age Day
February 11 Foundation Day
March 21 Vernal Equinox Day
April 29 Shōwa Day
May 3 Constitution Memorial Day
May 4 Greenery Day
May 5 Children's Day
July 16 (third Monday in July) Marine Day
August 11 Mountain Day
September 17 (third Monday of September) Respect for the Aged Day
September 23 Autumnal Equinox Day
October 8 (second Monday of October) Health and Sports Day
November 3 Culture Day
November 23 Labor Thanksgiving Day
December 23 The Emperor's Birthday