While this is surely not a dogma in the Orthodox Church, it is not mere speculation that the Prophet Jeremiah was assumed into heaven. Here are five reasons:

  1. Matt 16:14 lists Jeremiah alongside with Elijah as one of the prophets that people alleged Jesus to be. Clearly, the implication is that if people were accusing Christ of being some prophet of long ago re-entering the world, that it was common knowledge that he was bodily assumed. The fact that Jeremiah is paired with Elijah, a bodily assumed prophet, appears to vindicate this.
  2. 2 Macc 15:14-15 records Judas Maccabeus recounting a vision in which Jeremiah appears and encourages the Jews in their fight against the Greeks. Due to this event being recounted before the “Harrowing of Hell,” this is suggestive that it was popular Jewish belief at that time Jeremiah was not locked in Sheol before Christ’s coming, but was bodily assumed and thereby able to intercede for the living. Because no such claims are made about Onias, the deceased high priest who is also part of this vision, this may call into question the literal historicity of the source in question at least on this point. Nevertheless, it does preserve for us a popular Jewish notion about Jeremiah.
  3. Ecumenical Councils teach that he was sinless. (Council of Ephesus, Session 1, Par 54 and Council of Chalcedon, Session 1, v. 917–both councils quoting Saint Athanasius’ Against the Arians, Book 3, Par 33; cf Decree 6 of Council of Jerusalem 1672) While sinlessness does not guarantee bodily assumption (as Saints John the Forerunner and Demetrius have left behind relics), it at least plausibly gives a reason for it to occur.
  4. Legends surrounding Jeremiah’s body assert that it was incorruptible and at some point was moved by Alexander the Great to Alexandria. After that point there is another alleged tomb in Jerusalem. In any event from what I can tell the hagiographies ascribe miracles only to the tomb itself–the whereabouts of the body are unknown. There is no agreed location of the tomb, let alone his relics. This implies like the Theotokos, his body was laid to rest for a time (likely much longer than her) and then was bodily assumed.
  5. Saint Gregory Palamas teaches Jeremiah’s assumption quite plainly: “There were many resurrections before Christ’s resurrection, and similarly, there were many ascensions before His ascension. The Spirit lifted up Jeremiah the prophet [Footnote 311], and an angel took up Habbakkuk. In particular, it is written that Elijah went up with a chariot of fire.” (On the Ascension, Homily 21:2; p. 171 in Venamin’s translation) One should note that Venamin speculates in the footnote that this is a corruption and speculates Palamas had Ezekiel in mind (see Ezek 8:3). One must note that no manuscript replaces Ezekiel for Jeremiah.

While the preceding certainly does not prove with certainty that Jeremiah was bodily assumed, it would at least make me not surprised to find out in heaven (God willing) he was in fact assumed before the second coming. As long as someone does not point to some source that there are widely agreed upon relics and traditions surrounding them I am not aware of (which is certainly possible), I’d consider this a harmless speculation. I am willing to retract it. But I’d wager the more we dig the more we’d find consistent traditions with that of Saint Gregory Palamas’ plain statement on the question.