Evros is one of the largest prefectures in Greece. It is part of the Thrace geographic region (Western Thrace) and includes the island of Samothrace in the northern Aegean Sea. The prefecture is approximately 150 kilometres (93 mi) long from north to south (excluding Samothrace). Its width varies from 70 to 100 kilometres (43 to 62 mi) from east to west. Its most important rivers are the Evros and its tributary, the Arda.

The Rhodope Mountains occupy the west and northwest of the prefecture. The south of the prefecture is surrounded by the Aegean Sea. The Evros Valley is flat, while the island of Samothrace is mountainous.

The coastal areas of the prefecture have a predominantly Mediterranean climate, while the northern parts and the mountainous areas have a colder continental climate. Evros is home to the Evros Plain, the largest in Greece.

Evros is a lowland region, 10.3% of which is mountainous; however, 62.4% of the vast plains constitute a large part of cultivated land. The Evros River, its tributaries, and numerous irrigation canals contribute to the creation of arable land.

As part of the Department of Thrace, the territory of the Evros Prefectural Government follows the fate of all of Thrace. In 1821, the districts of Evros such as Lavra and Samothrace revolted. However, integration into Greece did not occur until 1920, when Bulgaria was forced to cede Thrace to Greece under the Treaty of Neuilly. It was initially part of the Prefecture of Thrace, but the prefecture was divided in 1930 into the Prefectures of Xanthi, Rhodope, and Evros. During the Greco-Turkish War of 1919–1922, many refugees arrived in Evros, and new towns such as Orestiada were built. The Evros River valley has flooded several times, the most recent floods occurring in 2005, 2006, 2014 and 2021, when multiple and largest floods of recent decades occurred.