The area was settled in the prehistory, and, as the Western Dvinaalways has been an important waterway, there are multiple archaeological sites in the district. The fortress of Porechye is first mentioned in 1499, and since 1514 it belonged to the Grand Duchy of Moscow, at the border with the Grand Duchy of Lithuania. In 1580, after the Livonian War, the area was transferred to Poland, where it was included into Vitebsk Voivodeship. In 1667, according to the Truce of Andrusovo, it was transferred back to Russia. Subsequently Porechye developed as an important trading post since it was located at the intersection of roads connecting Saint Petersburg with Kiev and Moscow with Riga. The Kasplya was navigable until mid-19th century, and Porechye sent ships to Riga. Later, it lost its trade important, since the Kasplya became more shallow, and the railway between Moscow and Riga went via Velikiye Luki, far from Porechye. In the course of the administrative reform carried out in 1708 by Peter the Great, the area was included into Smolensk Governorate and remained there until 1929, with the exception of the brief periods between 1713 and 1726, when it belonged to Riga Governorate, and between 1775 and 1796, when Smolensk Governorate was transformed into Smolensk Viceroyalty. In 1776, Porechye was granted a town status, and Porechsky Uyezd with the center in Porechye was established. On 19 November 1918, Porechye was renamed Demidov, to commemorate the bolshevik Yakov Demidov, who was the chairman of the Uyezd Communist Party Committee and was killed during the Russian Civil War. Porechsky Uyezd was renamed Demidovsky Uyezd. In 1927, Demidovsky Uyezd was abolished. On 12 July 1929, governorates and uyezds were abolished, and Demidovsky District with the administrative center in Demidov was established. The district belonged to Smolensk Okrug of Western Oblast. On August 1, 1930 the okrugs were abolished, and the districts were subordinated directly to the oblast. On 27 September 1937 Western Oblast was abolished and split between Oryol and Smolensk Oblasts. Demidovsky District was transferred to Smolensk Oblast. Between 1941 and September 1943, during WWII, the district was occupied by German troops.
In Demidov, there are enterprises of timber and construction industries.
Transportation
Paved roads connect Demidov with Smolensk, with Nevel via Velizh, and with Rudnya. There are also local roads with bus traffic originating from Demidov. The closest railway station is in Rudnya, on the railway connecting Smolensk with Vitebsk.
Culture and recreation
A couple of dozens of 18-19th century buildings survived; they are designated cultural monuments. One of them is the Dormition Church, built between 1852 and 1861. Several monuments to soldiers and civilians killed during the Russian Civil war and during WWII has been also designated historic monuments.
