The Known Lands
Polytheism is the belief in many gods, although as you have read, there is but One God dealing with the Known Lands. However, this does not make idolatry impossible. Idol worship and pagan worship is worship in a polytheistic sense. Their are two polytheistic movements in the Known Lands: Oerthism and Olympianism. Also, worship of the Ancients or the First Ones (or founders) is also included in some aspects.
Oerthism The original Polytheistic model of the Known Lands until the arrival of the Bretonia in Ancient Times was Oerthism (also known as the D&D pantheon). Oerthistic clerics still exist, but they are pretty much underground when other religions such as the Path of Light, the Holy Light, and Christianity has taken prominence. Oerthists do not have places of worship any more except for hidden temples.
The Deities worshipped include:
1. Bahamut) 2. Boccob 3. Corellon Larethian 4. Ehlonna 5. Erythnul 6. Fharlanghn 7. Gruumsh 8. Heironeous 9. Hextor 10. Kord 11. Kurtulmak 12. Lolth 13. Moradin 14. Nerull 15. Obad-Hai 16. Olidammara 17. Pelor 18. St. Cuthbert 19. Tiamat 20. Vecna 21. Wee Jas 22. Yondalla 23. Dennari
Their domains are recounted in the Deities and Demigods supplement for the Dungeons and Dragons 3rd edition game.
Olympianism has come to the Known Lands with the arrival of the Bretonia. It’s a pagan idol religion that comes from the people of Hellas, or the Ancient Greeks. The pantheon is tight, but worship is underground. Most Olympian clerics all look to Zeus, although the others are often worshipped. The pantheon includes:
1. Zeus 2. Aphrodite 3. Apollo 4. Ares 5. Artemis 6. Athena 7. Demeter 8. Dionysus 9. Hades 10. Hecate 11. Hephaestus 12. Hera 13. Hercules 14. Hermes 15. Hestia 16. Nike 17. Pan 18. Poseidon 19. Tyche
Their domains are recounted also in Deities and Demigods.