Which book, being the first of three volumes of the epic novel "The Lord of the Rings", is where the Old Forest makes its first and main appearance?
Old Forest:  Its first and main appearance in print was in "The Fellowship of the Ring", especially in chapter VI, which is itself titled "The Old Forest". The Fellowship of the Ring: The Fellowship of the Ring is the first of three volumes of the epic novel "The Lord of the Rings" by the English author J. R. R. Tolkien.
The Fellowship of the Ring