The closure went ahead despite several protests by locals, who expressed concerns about the economic impact of the move.
Soldiers have been based in Longford barracks since the late 1700s, but that long military connection has now come to an end.
The 130 troops marched through the streets of the town for the last time this afternoon, before they were relocated to Athlone.
Longford native and former Taoiseach Albert Reynolds attended the closing ceremonies.
Relatives of soldiers and residents conducted an intensive campaign before Christmas to keep the barracks open. However, the efforts of the campaigners were unsuccessful.
Troops from five military installations faced worrying transfers following October's Budget.
Over the last few days, posts in Lifford and Letterkenny have been shut down and Monaghan Barracks has also closed.
