The Elemental Planes are all Demiplanes, and there are a lot of them. The Elemental Planes are exceptionally hazardous for People to enter, for they are realms comprised mostly of that element; crossing into the plane of Stone can prove instantly fatal to anything not able to breathe rock. Worse, there is no “single” elemental demiplane for any element – all have dozens if not hundreds of minor little ones, where the greatest of those within are akin to the Gods of that space.
The Elemental Planes are Acid, Air, Earth, Fire, Frost, Lightning, Poison, Stone, Sand, Smoke, Spirit, Sun, Thunder, and Water. Elementals live within the wholeness of their element, and there are birds, beasts, fish, and people that live and exist within them. There is a frequent use of the term Force as an Element, but it is not properly so.
Elementals are the total masters of these regions. The Pale is also filled with innumerable pocket dimensions, some lived in, others untouched or unclaimed, but very few ever stumble on one for the Veil hides them as it surrounds them. Gob, Peralda, Djin, and Necksa all make their homes in Demiplanes within the Pale, from whence come the many incredible elemental beings. Those four, in particular, are considered the Rulers of the Planes, and direct children of Powers That Be.
Often counted as an element is Void (a direct conduit to The Void), but not a safe one. Don’t open a passage there elementally. It never ends well. This may be why no spells truly use it – no one has survived the experience, since the caster is always subject to the Void themselves, and nothing can control or direct the Void except for the Void itself – even the Pale. Also, no one has ever seen a void elemental, or even verify if there is such. Even spheres of annihilation don’t connect there.