The Counts of Montaigu were 12th century nobles of Lower Lotharingia who were closely associated with the Counts of Duras and Clermont. This particular place called Montaigu (Mons Acutus, pointy mountain) 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 exists upon the mountain on which it was built.
The Counts of Montaigu were also lords of Rochefort. Rochefort is a municipality in Namur, and these holdings passed by inheritance to the Walcourt family, who married into the family of the 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 original Counts of Clermont appear to have originated with a Widrich (d. before 1062), father of Ermengarde, wife of Gozelo I, but it passed on to the Counts of Montaigu after Giselbert, Count of Clermont.