The type species is H. castanedaii, found in sediments of the La Victoria Formation, part of the Honda Group in the department of Tolima in Colombia.

[1] In 2018, Carrillo et al. described a partial skull and mandible of a second species H. miyou from the Castilletes Formation in the Cocinetas Basin of northern Colombia,[2] and estimated the body weight of the animal at 6,456 kilograms (14,233 lb).

[3] The remains of Hilarcotherium castanedaii were discovered by José Alfredo Castañeda, who found them in the Malnombre Creek in the Hilarco village located near the town of Purificación, in Tolima.

This consists of fragments of skull, a partial jaw, the vertebral ramus of a dorsal rib, a complete left humerus and an incisor tooth associated.

The jaw missing the incisors, the crown of the fourth premolar and the left mandibular ramus, but has the roots of the teeth of the right side and a broken canine with an oval cross section.

[1] Analyses performed with his molars and humerus indicate that weight range of H. castanedaii would be between 1,187 and 1,369 kilograms (2,617 and 3,018 lb), which would be comparable to the modern black rhinoceros, close to 4 metres (13 ft) in length.

Within this group, Hilarcotherium shares with Xenastrapotherium, Uruguaytherium and Granastrapotherium the lower canines that are horizontally inserted into the jaw, in addition to the characteristics of the molars (without labial cingulum, an inner protuberance of the molars), indicating that Hilarcotherium and the others genera already mentioned belongs to the subfamily Uruguaytheriinae, a group that colonized the equatorial region of South America during the Miocene until their extinction in the middle of such period, in contrast with other astrapotheres only known in the south of the continent.