The main event was held in Knin, the centre of the Serb rebellion in 1991-1995, and it included a parade of army units, veterans, police and firefighters.
According to data from the Sibenik-Knin County Police, about 8,000 people attended the celebrations in Knin, braving a temperature of 41 degrees Celsius in the shade.
A pop concert was scheduled for the evening and the event will be rounded off with a fireworks display at 11 pm.
A military air show was held in Zadar, and hundreds of pigeons were released in Vukovar to fly to Knin.
In Pula, war veterans, military and police personnel, firefighters and local government officials took part in the fifth Istria County Veterans Parade through the city centre.
The 21st equestrian marathon of Arabian horses set off on a four-day 250-kilometre ride from the village of Voloder near Kutina in honour of the Kutina Battalion of the 125th Home Guard Regiment. The riders are expected in Jasenovac on Sunday evening to pay tribute to the Homeland War victims there.