A slottslän (Finnish: linnalääni) was a type of secular^{[note 1]} administrative division throughout the Kingdom of Sweden from late 13th century to 1634. The administrative center was a castle. Slottslän were divided into municipalities and administrators. The term slottslän can be translated as "castle fief". Although the word "län" literally means fief, in Sweden it is translated as "county" and in Finland as "province".

There existed multiple different types of slottslän, there existed pantlän, which could be assigned to a lord as compensation for a loan to the crown, until a repayment was done. There also existed kronolän, which were managed by an advocatus, if the advocatus was a military commander, would be referred to as a "hövitsman", which was a capitaneus, they were ordered to deliver and report surplus profit to the crown, however sometimes a fixed sum was to be delievered annually, where the advocatus got to retain some profit. There also existed län which were granted to noblemen for their services to the King.^[1]

Slottsläns were established by Birger Jarl to replace the lething system in the latter-half of the 13th century.^[2] Slottsläns were disbanded in 1634 following Axel Oxenstierna's land reform and replaced with provinces.^[3]