An “downtowner” is someone who inhabits the “downtown” section (often, but not always, located to the south) of a geographical area. “Down-towners” was cited in print in 1827, when it referred to Providence, Rhode Island. A May 1844 citation of “down towners” referred to Manhattan.
 
Similar Manhattan geographic nicknames include “uptowner,” “East Sider” and “West Sider.”
   
 
(Oxford English Dictionary)
‘down-ˈtowner n. one who lives in or frequents the down-town part of a city.
1830 J. F. Watson Ann. Philadelphia 244   They were the Achilles and the Patrocles of the ‘downtowners’.
1887 Courier-Jrnl. (Louisville, Kentucky) 8 May 12/5   Jay Gould has set down-towners to eating snails.
 
18 April 1827, Literary Cadet and Rhode-Island Statesman (Providence, RI), pg. 1, col. 3:
THE BLUE POINTERS.—At the south western extremity of this town, there used to reside a distinct race of beings, ‘yclept Blue Pointers; and isolated as they were, their habits, manners and customs, varied very materially from those of their neighbours, the up-streeters, the up-towners, the down-towners, Ship-streeters, and up-hillers.
(...)
But if the Blue Pointers had to contend with their vindictive foes, they also had their times of retaliation, and thrice luckless was that unhappy wight of a down-towner, or up-streeter, who happened to wander within the boundaries of the Blue Pointers’ dominions.
 
Google Books
Historic Tales of Olden Time:
Concerning the early settlement and progress of Philadelphia and Pennsylvania: for the use of families and schools: illustrated with plates
By John Fanning Watson
Philadelphia, PA: Published by E. Littell and by Thomas Holden
1833
Pg. 159:
They were the Achilles and the Patroclus of the ” downtowners.”
 
29 June 1835, The Adams Sentinel and General Advertiser (Gettysburg, PA), pg. 3, col. 5:
If they were caught below Market-street, they were in danger, in the Border wars of that day, of being pelted with brick-backs as up towners, or if above Market-street, they ran the same risk as being down towners. In truth between the up towners and down towners of that day, we well recollect, it was no easy matter fo a boy to escape a broken pate.
Newburyport Herald.
 
16 May 1844, New-York (NY) Commercial Advertiser, pg. 2, col. 6 ad:
All ye Wall Streeters,
PEARL STREETERS, UP TOWNERS AND DOWN TOWNERS, would it not be well for you to buy your stationary at SHEPARD’S where you can buy letter paper at 5d, 7d, 10d, 14d, and 18d per quire.
 
Google Books
New York in Slices
By George G. Foster
New York, NY: William H. Graham
1849
Pg. 67:
A regular down-towner surveys the kitchen with his nose as he comes up-stairs—selects his dish by intuition, and swallows it by steam and the electro-galvanic battery.
 
OCLC WorldCat record
The Downtowner. Why staggered hours.
Author: Down Town Association of San Francisco,
Publisher: San Francisco, The Association. 1951.
Edition/Format:   Book : English
 
OCLC WorldCat record
The downtowners : people who live in central Toronto, where they work and how they get there.
Author: Toronto (Ont.). Planning and Development Dept. Research and Information Section.
Publisher: Toronto : The Section, 1982.
Series: Research bulletin / City of Toronto Planning and Development Dept., Research and Information Section, no. 20
Edition/Format:   Book : English
Summary:
Results of a survey of downtown Toronto residents; survey conducted by students from the Urban and Regional Planning Department, Ryerson Technical Institute in 1981.