The Counts of Montaigu were 12th century nobles of Lower Lotharingia who were closely associated with the Counts of Duras and Clermont. Montaigu (Mons Acutus) was a castle located on the river Ourthe, opposite Marcourt near La Roche in the Ardennes. The castle of Montaigu has been mostly destroyed, but a chapel dedicated to Saint Thibaut still resides the mountain on which it was built. The Counts of Montage also held the title of Lord of Rochefort. Rochefort is a municipality in Namur, and these holdings passed by inheritance to the Walcourt family, who married into the family of Counts of Chiny, particularly Louis III.
The Counts of Montaigu were:
Cono I and his sons participated in the First Crusade with Godfrey of Bouillon. Thierry appears to have given up the countship of Montaigu although his great-grandson Thierry IV appears to have claimed dominion over three villages in the County of Montaigu.
The Counts of Clermont appear to have originated with a Widrich (d. before 1062), father of Ermengarde, wife of Gozelo I, and passed on to the Counts of Montaigu through either marriage to a daughter of or sale by Giselbert, Count of Clermont.