He was the son of Count Otto II of Rietberg and his wife Adelheid of Lippe.
He inherited the County of Rietberg when his father died on 18 July 1389.
He was buried in the family grave of the Counts of Rietberg in Marienfeld Abbey.
He shared a tomb stone with his wife Irmgard: In English translation: On 24 April 1399, he married Irmgard (d. 24 March 1426), a daughter of John of Diepholz (d. 1422) and Kunigunde of Oldenburg.
With her he had three children: Some sources say that Conrad IV was also married to Beatrix of Bronckhorst (d. 1392).