I left this on the comments of Chapter 87, but I'll put it here too. Some of the chapters seem to be linked, and there's a lot of locations (and years) that are recurring.
So because I like to over-analyze the most random things, I went ahead and made a Google spreadsheet noting every single chapter's location and year so far.
So, here we go! Still have to fill in chapter titles, but... eh. Note, I used "XX" to note basically "nationwide" areas, and "??" for unknown. Also, I have zero idea where Ishiyama is.
Some interesting takeaways: Most of the series takes place in Tokyo and Hokkaido, with a particular focus on Sapporo and the Suginami Wards. 28 are in Hokkaido for sure, with four more (Yamahana and the Chuou Line Overpass) being maybe Hokkaido. (There's a Chuou Ward in Tokyo, so that could go either way I think?) 25 are in the greater Tokyo area, with 14 specifically in Suginami Ward. Otherwise, most locations appear at least twice...
Except Kouchi City, which is the only city that's specified from a totally unconnected prefecture. Like seriously, just feels out of place. Even Saitama and Kanagawa, the other one-shots, are just listing the prefectures instead of cities?? I dunno, feels weirdly specific.
Meanwhile: there's 13 chapters set in 1998. 8 are set in 2013, so that's the next most common year. The earliest year is 1970, but not much happens in that (it's a kid who says he sees ghosts when he closes his eyes). However, 1975 is from Chapter 30, which ties into Chapter 7 of the very original series. (On that note, I think "Doutou" is the name for the east side of Hokkaido rather than a specific city.)
And then there's the year 2020... Two stories use it. And 67, "Venom Drinker", features a mask that grins when bad things happen. So it could be a reference to some nebulous event...
Or it could be a reference to Covid in 2020. The old man mentions an earthquake, and the first story with the mask was in 2011, so that could've been the 2011 earthquake/tsunami. And this volume seems to have been published near the start of Covid, so... it's possible.
Anyways, the spreadsheet has the dates/locations listed. Anyone who wants to use this to analyze for connections, be my guest! I set it so anyone can edit it, so feel free to add notes.