Well, it’s preferred form in its lair in the sewers under Derry is of a massive female pregnant spider, but it’s true form is the Deadlights, which don’t exist in our universe, plus Pennywise is inherently male. Assigning gender to a shapeshifter is always a tricky thing, especially when IT is actually a malevolent ball of pulsating light.

In 11/22/63 Jake goes back in time to stop the Kennedy assassination using a sorta portal in time a friend of his found years before, however the moment you get sent back to is fixed. It’s always August of 1958, so before committing 5 years of his life to save Kennedy he needs proof that you can truly alter time. He does this by saving a family in Derry that gets murdered by their father on Halloween. (except for one son who Jake knows in the present, which is how he knew of the event.)

Derry is a violent town even when Pennywise is “asleep” it’s a part of the symbiotic relationship that the town and creature have with each other, just every 27 years or so it skyrockets even further. The point being that Jake hates it there, he spends two months waiting in Derry for the event (meeting Richie and Bev at one point) with the cover story that he’s in real estate looking for a location for a hidden buyer. To put off any suspicion that he isn’t there for that job he drives out to the old Ironworks (where Mike had his first encounter with IT) while there he notices several animal bones at the base of a fallen smokestack and then hears a voice in his head beckoning him to walk inside and forget about his mission and the past, that maybe there’s another portal in here that’ll take him somewhere even newer. It’s worth noting that Jake is there only a short time after the Losers beat IT during the 57/58 cycle. So Pennywise is in its less active state.

Jake would later hear that voice again when he heads to Dallas while looking at the Texas book depository where Oswald would shoot the President in a few years time and several decades before for Jake.

King makes several allusions about Dallas and Derry being extremely similar in nature, with a malevolent nature about them. That’s not to say that there’s an IT in Dallas too, but Jake thinks at one point that he wouldn’t be surprised if there’s a portal in Dallas similar to whatever was in that smokestack.