No release dates announced yet. The new PV is here. This announcement comes as the current season finale aired today. Check out the Crunchyroll article for additional information. Source manga synopsis from AniList:
The setting is Taisho era Japan. Tanjirou is a kindhearted young boy who lived peacefully with his family as a coal seller. Their normal life changes completely when his family is slaughtered by demons. The only other survivor, Tanjirou’s younger sister Nezuko, has become a ferocious demon. In order to return Nezuko to normal and get revenge on the demon that killed their family, the two of them depart on a journey. From a young talent, an adventure tale of blood and swords begins!
I haven’t read/watched Demon Slayer, but I think these movies should be the end of the main story if I am reading articles correctly. Congrats to all the fans of the series for getting a complete adaptation. That doesn’t happen too often.