The archaeological finds are evidence of the fact that the Cetina area has been inhabited since prehistoric times. A number of finds from the end of the Copper Age to the Middle Bronze Age are attributed to the so-called Cetina culture. Suitable geographic position, caves, hills and fertile valleys have preconditioned the development of agriculture as well as the development of cattle breeding on the mountain slopes. The natives, members of the Illyrian tribe Delmates, appeared in the area during the Bronze Age and their development continued until the Romans had arrived. Although the Delmates persistently opposed the Roman authorities, numerous insurrections were successfully repressed. After the fall of the Roman Empire, barbarians repeatedly invaded the area. At the beginning of the 7th century, Croats came from White Croatia (the Vistula region in today’s Poland) and settled in the region of Dalmatia. The archaeological finds dating back to the 7th – 9th century period serve as evidence of the Christianisation process through the influence of Franks. This was the time of the foundation of the first Croatian principalities. In the later period, when a kingdom was founded, fortified Sinj became the centre of the Cetina County. As the princes grew in power and influence, the Cetina Principality was founded. The title of princes of Cetina was first acquired by the Šubic princes and from 1345 it belonged to the Nelipic princes. The Franciscans of the Bosnian Vicary were encouraged by Prince Ivan Nelipic to come to Cetina, the town at the foot of Sinj fortress. There they built St Mary’s church as well as the monastery, which was plundered and burnt by the Ottomans in 1492. In 1513 Sinj fell into Ottoman hands, up until 1686, when it came under Venetian rule. The Ottomans, however, were still attempting to win back Sinj. The most significant battle was fought in 1715, when 700 defenders of Sinj repulsed an attack of tens of thousands of Ottomans. The disordered Ottoman army, weakened by hunger and the outbreak of dysentery, left the Cetinska Krajina Region.
Sinj remained under the direction of Venetian governor until 1797, and from that year to 1918 it was under Austrian rule. During this period the Town was also under French domination, but this was only briefly.
After the Kingdom of Serbs, Croats and Slovenes, and then the Kingdom of Yugoslavia, the Independent State of Croatia, the Italian occupation and the communist Yugoslavia, Sinj has finally become part of the independent and sovereign Republic of Croatia.The Day of the Town of Sinj is celebrated on August 15. On that day Assumption of the Madonna, the patroness of Sinj, is celebrated as well.