Mecheye
I cannot find any information on this location existing on-map as a neighborhood, though there are some conflicting sources. See below for details!

The first instance I found with both the railroad junction AND the proper "Pacific Junction" labeling was in this map by Snyder from 1886 (https://www.loc.gov/item/2013593088/)

You can see on that map that it has a "P.O" written underneath it, indicating that this was a post office. However this map by Flower from the same year does not list Pacific Junction as a Cook County post office in the upper right corner, nor does it even show the railroad junction at all (https://www.loc.gov/item/2013593075/)

However, this website lists this post office as existing via their transcription of the Post Office Directory of Illinois 1884 (http://genealogytrails.com/ill/postoffices.html)
I can't find a copy of this book online to verify.

All that being said, there is some idea that this DID exist as a place according to "Chicago and its Suburbs", written by Everett Chamberlin in 1874. (https://www.yumpu.com/en/document/view/53765137/chicago-water-works). Page 436 indicates that a town named "Pacific" was being built in the general area of Pacific Junction, however none of the maps I linked here show that town save the "Pacific Junction P.O." as stated earlier in Snyders map.
The book mentions a few people involved in its creation: "Messrs. Warren, Keeney & Co, Judge Gookins, and J. F. Sinclair & Co."

A cursory search of those names brougt up another mention of "Pacific"  found via Archive.org (https://archive.org/stream/oursuburbsresume00chic/oursuburbsresume00chic_djvu.txt)
This mentions much of the same, but also includes some street names that I cant seem to match up to what is listed in other maps.

At this point I'm thoroughly lost.

I managed to find verifiable land plots and boundaries for the nearby defunct neighborhoods of Garfields and Simons, but nothing on this one.

Can anyone lend a hand?