During his childhood, Dietrich married a distant cousin, the Countess Adelheid of Oldenburg-Delmenhorst, daughter of Oldenburg Count Otto IV of Delmenhorst, for reasons of succession and uniting the hereditary fiefs. Countess Adelheid is presumed to have died in 1404. In 1423, Dietrich married again, to Helvig of Schauenburg (born between 1398–1400 and died in 1436), widow of Prince Balthasar of Mecklenburg and daughter of the murdered Duke Gerhard VI of Schleswig and Holstein and his wife Elisabeth of Brunswick and, thus, sister of the reigning Duke Adolf VIII. All his legitimate children were born by his second wife.