See Leon and Graham about the Ents & Huorns

There were 50 Ents still alive in Middle Earth in the 3rd Age.

There were no young Ents, as the Entwives had been lost during the 2nd Age, after their gardens were destroyed by Sauron.  So the Ents could no longer reproduce.

By the 3rd Age Treebeard, Leaflock & Skinbark were the only remaining Ents from the Elder Days. Many of the younger ones were growing 'treeish', being less active & more like trees. The forest of Fangorn was the last of their remaining domains. Beechbone was still an active Ent among the younger Ents.

The Hourns were trees that still had an awareness of the outside world within the forest. But they needed herding by the Ents to become active. They hated all living things except the Istari & Elves & would kill anything that went into the forests, if they could catch it.