In the reign of Ivan the Terrible the Sevsky Kremlin was fortified, garrison reinforced by guard Cossacks, who created a Cossack sloboda here. In the middle of the 17th century a Sev fortress was included in the system of newly created defensive guards along the south-western borders. The convenient location contributed to the creation of a strong fortress here, which played a significant role in the history of Russia. Sevsk was known as a major shopping center not only in Russia, but also in the West. In 1634, the siege of Sevsk / defense of Sevsk from the Poles played an important role in ending the Smolensk War. After 1683 and the city grew many times at the expense of streltsy and other service people, sent here from Moscow after Streletsky Revolt (1682)/ streltsy riots. At the end of the XVII century, a silver coin was minted in Sevsk for Ukrainian territories that became part of Russia — Sevsk Czechs. In 1687 at Sevsk, the 32nd Chernihiv Colonel was beheaded Grigory Samoilovich (son of hetman a Ivan Samoilovich).
In the XVIII century, the defensive importance of Sevsk as a border town weakened, as the borders were moved to the south and west. It organizes the civil administration. The city was granted a coat of arms and a general development plan. Military people are settling on the outskirts of the city. In Sevsk and its environs, there are still Streletskaya, Pushkarnaya, Soldatskaya Sloboda, and the village of Reitarovka.
With the division of Russia into provinces, Sevsk was included in the Kiev Governorate, in which in 1719 became the center of Sevsk province, which included 9 cities: Sevsk, Trubchevsk, Bryansk, Karachev, Kromy, Rylsk, Putivl, Nedrigailov and Kamenny with their districts (uyezds). In 1727 Sevsk was transferred to Belgorod province, divided into three provinces, of which Sevsk province was the most populous (out of the 700 thousand population of the province, it accounted for 300 thousand).
In 1778 Sevsk becomes the center of Sevsky uyezd as part of Orel Viceroyalty. At this time, it was decided to rebuild the city according to a new plan, breaking it into regular squares. The inhabitants of the city were engaged in crafts, trade and Yamsky craft.
In the 1880s, the first railway line ran through Sevsky uyezd, but Sevsk itself was left out of it, which affected the development of industry and trade. At the same time, much has been done in the improvement of the city: water supply was carried out, the central streets were gas-lit, the main street was paved with cobblestones. In the eastern part of the city, on the high bank of the Seva, a building of the zemstvo council was built. In the north-western part of the city in 1913, a large two-story building was erected, specially designed for the Sevsky Real School, established in 1909. The school became one of the cultural centers of the city, where literary evenings were held, concerts were arranged, and amateur performances were staged. In 1917, the mathematician Ivan Petrovsky, future rector of Moscow State University, graduated from the school.
Architectural monuments include the remnants of defensive walls of the medieval fortress and the churches of Kazan Virgin (1760), Ascension (1765), and Sts. Peter and Paul (1809). Sevsk used to have two cathedrals, one dating to 1782 and another to 1811. Both cathedrals were destroyed during Stalin's rule, but their bell towers still stand.
Брянская областная Дума. Закон №13-З от 5 июня 1997 г. «Об административно-территориальном устройстве Брянской области», в ред. Закона №4-З от 5 февраля 2014 г. «О внесении изменений в отдельные законодательные акты Брянской области». Опубликован: "Брянский рабочий", №119, 24 июня 1997 г. (Bryansk Oblast Duma. Law #13-Z of June 5, 1997 On the Administrative-Territorial Structure of Bryansk Oblast, as amended by the Law #4-Z of February 5, 2014 On Amending Various Legislative Acts of Bryansk Oblast. ).
Брянская областная Дума. Закон №69-З от 2 ноября 2012 г. «Об образовании городских административных округов, поселковых административных округов, сельских административных округов, установлении границ, наименований и административных центров административных округов в Брянской области». Вступил в силу 1 января 2013 г. Опубликован: Информационный бюллетень "Официальная Брянщина", №16, 6 ноября 2012 г.. (Bryansk Oblast Duma. Law #69-Z of November 2, 2002 On the Establishment of Urban Administrative Okrugs, Settlement Administrative Okrugs, Rural Administrative Okrugs, on Establishing Borders, Names, and Administrative Centers of the Administrative Okrugs of Bryansk Oblast. Effective as of January 1, 2013.).
Брянская областная Дума. Закон №3-З от 9 марта 2005 г. «О наделении муниципальных образований статусом статусом городского округа, муниципального района, городского поселения, сельского поселения и установлении границ муниципальных образований в Брянской области», в ред. Закона №75-З от 28 сентября 2015 г. «Об изменении статуса населённого пункта посёлок Красный Ятвиж Клетнянского района Брянской области». Вступил в силу через 10 дней после официального опубликования. Опубликован: "Брянская неделя", №13, 8 апреля 2005 г. (Bryansk Oblast Duma. Law #3-Z of March 9, 2005 On Granting the Municipal Formations the Status of Urban Okrug, Municipal District, Urban Settlement, Rural Settlement and on Establishing the Borders of the Municipal Formations of Bryansk Oblast, as amended by the Law #75-Z of September 28, 2015 On Changing the Status of the Inhabited Locality the Settlement of Krasny Yatvizh in Kletnyansky District of Bryansk Oblast. Effective as of the day which is 10 days after the official publication.).