Omiš has been mentioned for the first time in the X. century.
Long time ago Omiš was fortified little town below castle Peovica (Mirabella) and farmed fields were all around. During tempestuous history  advantageous position of the town enabled the citizens to easily defend themselves. Once a chance for easier defense, nowdays a unique phenomena on Adriatic Coast. Historical centre, known as the old part of the town is situated on the eastern coast.
In Ancient times settlement had been situated more north than the one today, in the part called Baučići. It has been cosidered that the origin of the name of the town comes from Slavic word holm/hum which translated from Illyrian-Greek word onaion/oneon, which stands for hill, cam, point on a hill. The other explanation is that Oneum comes from the name of river Cetina, bacause the Greek colonists used to call river’s underflow Nestos.
During the Middle ages the town was called Olmissium, Almiyssium, and during the Venetian domination the town was called Almissa. Todays name comes from  medieval name.
With time and thanks to the development of industry and tourism, Omiš had developed. Area of the town, according to datas from the year 2001, counts 15 472 inhabitants. It is consisted out of these villages: Blato na Cetini, Borak, Čelina, Čišla, Donji Dolac, Dubrava, Gata, Gornji Dolac, Kostanje, Kučiće, Lokva Rogoznica, Marušići, Mimice, Naklice, Nova Sela, Town Omiš, Ostrvica, Pisak, Podašpilje, Podgrađe, Putišći, Seoca, Slime, Smolonje, Srijane, Stanići, Svinišće, Trnbusi, Tugare, Zakučac, Zvečanje.
Omiš has had a tempestuous and rich history which is seen along every step. Two very important fortesses, Peovica (Mirabella) built on limestone rock just above the town, and Starigrad (Fortica) built on top of Omiška dinara, serve as a reminder of glorious times when Omiš was a very important trade centre. Thanks to the forts they could defend themselves from invasions of Turks and Venetians. From these forts one can see the whole Brač’s Canal and canyon of Cetina. The centre of the town, as well as all the crooks, passes and villages wealth with remains of former towers and castles because domestic population defended its proprety and estate from enemies. In ”De administrando Imperio” from 10th C, the work of Konstantin Porfirogenet, we find the first mention of circumstances on this territory. According to some preserved documents from The Middle Ages, Omiš was an important centre of Neretvanska Kneževina, during government of king Petar Krešimir IV in the 11th C it belonged to the Old Croatian State.
In medieval period most of the citizens were pirates. This was a very important way of property acquisition. In those days this was a sort of a economy that led to the prosperity of the town. Pirates from Omiš were wll known and everyone was afraid of them. This was so thanks to the agility of pirates but also thanks to their quick and light vessels.
During the most glorified period, on the throne of the pirates in Omiš were the counts of a clan Kačić. For more than two hundred years they had guided the assults on galleys of the Pope, on the merchant ships of powerful Venice, Dubrovnik, Split and others. Their assults were the main reason for frequent wars and conclusions of an agreement that ended with them paying tribute to the Omiš’s pirates in exchange for peaceful sail. But, every agreement with pirate was not longlasting, so there were two crusaders’ wars against them. The first war started in 1221 under the board of Pope Honorije III ended with pirates’ triumph. The second crusaders’ war started under the board of Venetians in 1286. This war was the beginning of the fall of a great clan of Kačić. Pirates had lost this war and it meant the end of thir domination in Omiš.
After this period, rulers of Omiš alternate, pirates were still present, but they have never reashed former glory. During history, Omiš had been under the rule of the counts of Šubić, brothers Horvat, Bosnian squire Hrvoje Vukčić Hrvatinić, ban Ivaniš Nelipić, family of Matko Talovac and Bosnian duke Stjepan Kosača.
After 1409, the year when Ladislav Napuljski had sold Dalmatia to the Venetians, in 1444 Omiš acknowledges the rule of that country too. As a part of the same constitution Omiš stays untill 1797.
In period from 18th C to 19th C it was governed by the Austrians, then shortly by the Frenchs, and then again by the Austrians. After Great Wars in Europe, when lots of old empires lapsed and many small countries came into existance, Omiš was, together with Dalmatia, joined to Croatia and in 1991 became the town of autonomous  Republic of Croatia.
All this is documented in the sole of the town, in its old part. This is not a word on the paper, it can all be seen while sightseeing our old and noble town.