Family
In 1785, Armfelt married Countess Hedvig Ulrika De la Gardie (1761–1832), daughter of Count Carl Julius De la Gardie and his wife, Countess Magdalena Christina Stenbock.
They had the following eight children:
Countess Maria Magdalena Catharina Augusta Armfelt, (1786–1845), married Count Axel Adolf Piper-Ängsö (1778–1827) and had issue;
Baron Gustaf Fredrik Armfelt (1788–1789);
Baron Carl Armfelt, born and died 1788;
Baron Magnus Armfelt, born and died 1788;
Count Gustaf Magnus Armfelt, (1792–1856), major-general, married Louise Cuthbert-Brook, Lady of Joensuu (1801–1865);
Count Alexander Armfelt, (1794–1876), captain, Finnish minister secretary of state, privy councillor, married firstly Baroness Siri Oxenstierna (1801-1841); married secondly Aline Demidov (1808-1898) and had issue from both marriages;
Baron Constantin Armfelt, (1796–1797);
Count Carl Magnus Wilhelm Armfelt, (1797–1878), married Baroness Adelaide Sohvia Vlhelmiina Karoliina von Stedingk (1802–1863; div. 1834); married secondly Ulrika Christina Vilhelmina Bohman (1818–1892), and had issue from both marriages.
From the affair with the actress Mademoiselle L'Eclair in Paris, Armfelt had an illegitimate son, Maurice L'Eclair (1780–1841). From the affair with Princess Wilhelmine, Duchess of Sagan, Armfelt had an illegitimate daughter, Countess Adelaide Gustava Aspasie (Vava) Armfelt (1801–1881). Maurice was knighted in 1816 in Sweden as Mauritz Clairfelt and became a general; Vava was adopted in 1812 into the Armfelt family. He also had an out of wedlock daughter with Princess Ekaterina Nikolaevna Galitzina (1764–1832), Princess Ekaterina Gagarina (1794–1835).