Crusell was born in Uusikaupunki (Swedish: Nystad), Finland, into a poor family of bookbinders. His grandfather, Bernhard Kruselius had learned the trade of bookbinding in Turku and Stockholm, then settled in Pori where he fathered nine children, including Crusell's father Jakob, who also became a bookbinder. In 1765, after Jakob completed his apprenticeship, he moved to Uusikaupunki and married Helena Ylander, but she died about one year later. In 1769 he married Margaretha Messman. The couple had four children, but Bernhard was the only one who lived to become an adult. Later in life Crusell described this period of his life, writing in the third person: