Leinster is one of the provinces of Ireland. It is in the southeast and east of the country, and it is part of Ireland. The province is made up of the three ancient kingdoms of Meath, Leinster, and Osraige. Following the Norman invasion of Ireland in the 12th century, the "fifths" of Leinster and Meath started to merge, mostly because of the Pale, which crossed both. This led to the creation of the modern province of Leinster. In the past, the kingdoms were split into a number of counties for administrative and judicial reasons. In the past few centuries, local government laws have led to even more subdivision of the historic counties.
Leinster has no official role in local government. However, it is an official part of Ireland and is on the ISO 3166-2 list as one of the four provinces of Ireland. "IE-L" is the code for Leinster's country sub-division in the United States. In the early results of the 2016 census, Leinster had 2,630,720 people, making it the most populous province in the country. The old flag of Leinster has a golden harp on a green background.