William I of Württemberg
On 24 January 1816, in Saint Petersburg, he married his first cousin, Grand Duchess Catherine Pavlovna of Russia (1788–1819), daughter of Emperor Paul I of Russia (1754–1801) and Princess Sophie Dorothea of Württemberg (1759–1828). The couple had two children:
Peter I, Grand Duke of Oldenburg
On 6 June 1781, he married Duchess Frederica of Württemberg, the second daughter of Frederick II Eugene, Duke of Württemberg and his wife, Friederike Dorothea of Brandenburg-Schwedt. Frederica's sister, Sophie, was the wife of Crown Prince Paul of Russia (the future Tsar Paul I. Peter and Frederica became the parents of two sons: August (born in 1783) and George (born in 1784).