The county was located in the south-eastern part of Greater Romania, in the southern Dobrogea region, known as Cadrilater.

[1] After the annexation of the Cadrilater to Romania, Durostor County, headquartered in Silistra, was established in the same year.

Durostor County, together with the rest of the Cadrilater, remained with Romania until 1940, when the Treaty of Craiova of September 7 returned to Bulgaria as an indirect consequence of Nazi German political pressure on the Romanian government.

The county's capital was the town of Silistra (sometimes referred to by an antiquated Romanian name, Dârstor).

On September 7, 1940, the former county (except for the north-eastern corner comprising Ostrov and Lipnița communes) with the whole Southern Dobruja was returned to Bulgaria (see Treaty of Craiova).