Adolph IX of Holstein-Kiel

Adolph IX (c. 1327–1390), numbered Adolf VII in the Kiel tradition, was the only son of Count John III the Mild of Holstein-Kiel, whom he succeeded in 1359 as count of Holstein-Kiel and Holstein-Plön. In 1362 he married Anna of Mecklenburg-Schwerin.

His long reign was mostly peaceful: in 1375 Archbishop Albert II of Bremen mortgaged him the Haseldorf Marsh, which was never redeemed and so stayed with Holstein. He died heirless in January 1390, after which the Rendsburg counts occupied his lands.