The Municipality of Neum, which belongs to neighbouring Bosnia and Herzegovina, divides the county in two parts which are connected only by the Pelješac Bridge.

The southern part of the county consists of Dubrovnik and the surrounding area, including the Pelješac peninsula, and the islands of Korčula, Lastovo, Mljet, Šipan, Lopud and Koločep.

The northern part of the county includes the Neretva Delta, the Baćina lakes north of Ploče, and a swath of hinterland near the southernmost slopes of Biokovo and around the hill of Rujnica.

Although the 9 kilometres-long stretch of coast belonging to Neum effectively makes the southern part of the county an exclave (disconnecting it from mainland Croatia) it is still connected with the rest of the country via the Pelješac Bridge.

The road connecting Dubrovnik to the rest of the country via Neum has one lane per direction and bus lines passing through Neum often make rest stops there so that passengers can take advantage of lower Bosnian taxes and purchase tobacco and alcoholic beverages as they tend to be cheaper there.