In attendance at the ceremonies, being held to commemorate Victory and Homeland Thanksgiving Day and Veterans' Day were top state officials including President Ivo Josipovic, Prime Minister Jadranka Kosor and Parliament Speaker Luka Bebic.
Church bells rang out to announce the start of the ceremonies.
Croatian war veterans organised a march and a motorcade through the town streets.
The military and police operation codenamed Storm began at 5 am on 4 August 1995, a Friday, and in only 84 hours Croatian soldiers and police liberated close to 10,500 square kilometres or one-fifth of the country's territory.
The 5 August 1995 liberation of the southern Croatian town of Knin carried special significance because since the summer of 1990 this town had been the centre of the rebellion of local Serbs.