The House of Olelkovich was a princely family from the Grand Duchy of Lithuania in the 15th and 16th centuries. Their main possession was the Duchy of Slutsk–Kapyl. They are sometimes known as Slutskys. They were descended from the Lithuanian Gediminids and Ruthenian Rurikids. According to the 1528 military census, the family was the fourth wealthiest magnate family in the Grand Duchy. However, its influence declined after the Union of Lublin (1569). The last member of the family was Sophia Olelkovich Radziwill (1585–1612), wife of Janusz Radziwiłł. She was elevated to sainthood in the Eastern Orthodox Church in 1983. As part of her marriage negotiations, she insisted on remaining a member of the Eastern Orthodox Church, despite her future husband's allegiance to Calvinism. She died in childbirth, as did the child. After her death, her considerable wealth and the Principality of Slutsk passed to the Radziwiłł family.

Kapyl is a town in Minsk Region, Belarus. It serves as the administrative center of Kapyl District. It is located 34 kilometers (21 mi) west-northwest of Slutsk and 90 kilometers (56 mi) south-southwest of the capital Minsk. In 2009, its estimated population was 9,900 based on the provisional figures from the 2009 census. As of 2024, it has a population of 9,985.