In 1637, after death of Bogislaw XIV he (was the last Duke of Pomerania) and after extinction of the Griffins’ ruler, the Brandenburg elector gave a decree about the inclusion of Middle Pomerania to Brandenburg. After the end of the Thirty Years' War, as the result of decisions of the Treaty of Osnabrück in 1648, Brandenburg March received Slupsk Earths (among other things), which were under direct rule of Hohenzollerns family for about 270 years. The actual occupation of admitted Brandenburgs earths succeeded after 1653. Slupsk was divided into two different administrative laws. The New City situated on left bank of Slupia River was found under the sway of the town council. The other part of the Old City, as the village, was a subject under the governmental jurisdiction. To 1720 the jurisdiction was exercised by headship of a village. After this date it was under the rule of landrat.

The first superior institution under which conclusive decision for Brandenburg Pomerania cities were made was since 1654 Directory with seat in Stargard. In the half of 18th century the Slupsk Town Council counted twelve people. Only the so- called first mayor (out of three) was vested publication of binding decisions. The mayor represented affairs of the city outside and was the member of Stargards Directory. Within a range of judicatures the city was completely independent, only in case of maritime law one invoked port-court, being situated in Kolobrzeg.

In 1740 Slupsk municipal authorities consisted of eight people: twain mayors, a secretary, a steward and four senators. It was a characteristic system for cities of the Prussian Kingdom. It was called municipality. From the end of 17th century counties (counties of territorial public administration) were begun to call districts. In 1724 a basic administrative reform was carried out. Brandenburg Pomerania was divided into two provinces; Stettin and Koszalin and other 24 districts. Slupsk administrative district was one of the biggest. The earthly local councilor who managed an administrative district was called a landrat. He was in an office of supervision of finance and had wide police authorizations.

The Prussian country acceded to internal reforms after a defeat with Napoleon's France in 1806. Especially crucial role happened to city law in 1808. According to this law, the city was administered by two self-governed bodies; a town council and a municipality. The first town council (legislative organ) was chosen in 1809; it counted 39 members and 13 substitutes. While municipality (executive organ) was chosen by town council, Slupsk municipality consisted of 12 people together with the mayor. The mayor was chosen once a 12 yrs. The members of the municipality were chosen once a 6 yrs. There were also some advisory select committees, so- called urban deputations, which dealt with some civil matters. An independent State-police was made and from 1874 a register office.

After 1808 town clerks missed powers within range penal jurisdictions. A state municipal court was created. After 1874 Slupsk transferred Prussian state port in Ustka. From this date weakness of existing legal relationships to Ustka settlement began. The economic (in cut off range)independence Ustka acquired in 1874, however, remaining legal dependences from Slupsk, became finally brought down in 1900. After 1815 Slupsk was a capital town of the greatest rural district in Prussia (2200 square kilometers). The relationships with organization of district-self-government were permanent to 1898. In this year Slupsk acquired the status of the city on independent administrative district laws.