Countess Armgard of Rietberg (also: Irmgard; died 13 July 1584) was from 1562 to 1584 Countess of Rietberg in her own right. She was also Countess of Hoya by marriage from 1568 to 1575 and Countess of Lippe by marriage from 1578 until her death.Armgard was the elder of two daughters of John II and Agnes of Bentheim-Steinfurt. Armgard married on 3 January 1568 Count Eric V of Hoya. He died on 12 March 1575.