Can someone give me some intel on the redmond barrens decline and glow city?

Glow City is a nuclear reactor that suffered a partial meltdown. It leaks radioactivity and is generally a smaller version of Chernobyl. However, despite the risks, a community of squatters installed itself around the reactor. They suffer from cancers, mutations and many health problems. A gang, The Rust Stilettoes, calls this place home.

The Redmond Barrens in general came to be during the Crash. The many IT companies went bankrupt, crashing the economy and then the local governement. Then poor people starting to move in and squat. The authorities stopped trying to fix the situation and abandonned it. It thus became a magnet for the poor and disenfranchised, turning into the Barrens.

Much of thanks. I figured it had to be something like that.

If I remember correctly, Glow City is also the domain of a toxic shaman named Burning Bones, who thrives on the rad count, right?

Nah. The radiation probably made him even more dangerous since one would assume he'd either attune to it magically, or have a Radiation Shield spell (T:W), or both.

When was glow city added to Seattle? I don't recall it from either of the Seattle books. Is it new with Runner Havens or was it added elsewhere?

The first edition Seattle Sourcebook had a paragraph on it on p.130. The same write-up was essentially copied into New Seattle. (p.65) However, there was a bit more Shadowtalk added to it there.