#it lore dump

There was a group of 200+ souls from the Old World who arrived in Derry in the 1700s and vanished within a year, leaving nothing but one burned out home when the next settlers arrived. This incident doesn't get explored in the original work besides as the first documented case of the cycle. (Theoretically, this is likely when the indigenous people of the area understood that something had to be done.)

The Kitchener Ironworks explosion of 1906 happened on an Easter Sunday. Over 80 children ran into the factory to find eggs. The workers had shut the whole place down, dousing all the kilns and stopping the churning gears. It still blew sky high and took the kids with it, raining chunks of child over half the town. This is a doubly important event because it was another case of a massive tragedy cutting Its feeding cycle short.

One egg survived the end of the novel - one single egg - and later births a creature known as Dandelo. This critter is admittedly only implied to be related to IT, but has the same psychic ability to feed off the strength of human emotions. Unlike IT, however, Dandelo feeds on laughter and amusement. It's worth noting that Dandelo is very quickly handled by the characters of The Dark Tower series, which suggests that Dandelo was, in many ways, an infant compared to the original It.

That confirms that IT could subsist off any strong human emotion - IT simply chooses fear for personal reasons, though the end result is always eventual death of the target.

IT avoids adults because an adult mind doesn't hold onto fear in the same shamanic respect as a child's mind. When children experience any emotion, they feel it much more powerfully than an adult - especially terror. This doesn't mean that IT isn't able to show Itself to adults (it turns into a doberman-headed monster for a Juniper Hill guard in the novel). IT simply isn't interested in them.

I personally theorize that IT isn't even purposeful about IT's possession of Derry - IT is not a migratory beast, besides in a cosmic sense, so IT likely has no reason to wander far from home.

The novel heavily implies that Earth isn't the first world that IT has feasted on - in fact, it's stated quite clearly that IT has done this many times before, and actually routinely hops between dimensions/planets/solar systems to stay away from Maturin and to feed Its insatiable appetite.

IT is less an evil entity and more an uncontrolled cosmic force that's finally broken free of the other cosmic force that used to keep IT at least slightly controlled.

The turtle's name is Maturin and it's honestly so beyond done with ITS shenanigans.

The turtle and IT are two sides of the same force, despite ITs hatred of Maturin. Though It delights in the turtle being dead in the second half of the novel, it's likely that neither IT nor Maturin are ever actually dead. But they can definitely be literal millions of years away from a comeback tour.