The Kingdom of Serbs, Croats and Slovenes was formed in 1918 and was initially divided into counties and districts (this division was inherited from previous state administrations).

In 1929, 33 oblasts were administratively replaced with 9 banovinas and one district, and the territory of the Syrmia Oblast was divided between the Danube Banovina, the Drina Banovina, and the Belgrade City Administration.

According to the 1921 census, all districts (Serbo-Croatian: srezovi / срезови) and administrative cities in the Syrmia Oblast had a dominant Serbo-Croatian-speaking population.

By religion, 7 eastern and central districts (Ilok, Irig, Ruma, Mitrovica, Stara Pazova, Šid, Zemun) were mainly Orthodox, while 3 western districts (Vukovar, Vinkovci, Županja) were mainly Catholic.

[1] Oblast included following districts: Besides these districts, several cities in the oblast had a separate status: The main cities and towns in the district were: Most of the mentioned cities and towns are nowadays in Serbia, while the towns of Vinkovci and Vukovar are nowadays in Croatia.