Clemens August von Galen was born on 16 March 1878 in Dinklage Castle, Oldenburg, Germany, the 11th of 13 children born to Count Ferdinand Heribert and Elisabeth von Spee.
His father belonged to the noble family of Westphalia, who since 1660 governed the village of Dinklage. For over two centuries his ancestors carried out the inherited office of camerlengo of the Diocese of Münster.
Clemens August grew up in Dinklage Castle and in other family seats. Due to the struggle between Church and State, he and his brothers were sent to a school run by the Jesuits in Feldkirch, Austria.
He remained there until 1894, when he transferred to the Antonianum in Vechta. After graduation, he studied philosophy and theology in Frebur, Innsbruck and Münster, and was ordained a priest on 28 May 1904 for the Diocese of Munster by Bishop Hermann Dingelstadt.