West Sider or Westsider

A “West Sider” (or “Westsider,” also lowercase “west sider” and “westsider”) is someone who inhabits the west side of a geographical area. “West-Siders” was cited in print in November 1850, when it referred to Milwaukee, Wisconsin. An 1851 citation of “West-siders” referred to Manhattan.
 
Similar Manhattan geographic nicknames include “East Sider,” “downtowner” and “uptowner.”
     
 
(Oxford English Dictionary)
West Sider, n.
orig. U.S.
An inhabitant of the west side of a city, esp. of the West Side of Manhattan.
1851 N.-Y. Daily Times 15 Feb. 8/3   It is known that there are many places of interest on this side of the Hudson… So please hurry up this ferry business, West-siders.
1855 Daily Cleveland (Ohio) Herald 26 May,  It will be necessary to wait upon the ‘West-siders’ for their part of the annual subscription.
1901 A. Ulmann Landmark Hist. N.Y. xi. 213   Most New-Yorkers..are either east-siders or west-siders, and know little of the other side of the town.
 
26 November 1850, Daily Free Democrat (Milwaukee, WI), pg. 2, col. 4:
SPRING STREET BRIDGE—AGAIN.—The floats that support this structure, have at last been raised, an to the great joy of the West-Siders, there is a prospect of a speedy completion of the repairs.
 
19 December 1851, Daily Register (Springfield, IL), pg. 2, col. 2:
Rockford (in this state) was settled in 1834 by G. Kent, who was the first white settler, and a west sider. Daniel S. Haight followed him the next year, and was an east sider.
(...)
Chicago Journal.
 
Google Books
History of Western Massachusetts:
The Counties of Hampden, Hampshire, Franklin, and Berkshire.
Volume II, Part III
By Josiah Gilbert Holland
Springfield, MA: Published by Samuel Bowles and Company
1855
Pg. 158:
They sent out to the people of Wilbraham, and told them that if they would all come in, and vote for Col. Worthington, they would all vote for a man to be selected from Wilbraham, as the second man on the ticket, and thus knock the West-siders out altogether.
 
17 January 1855, Cleveland (OH) Daily Plain Dealer, pg. 3, col. 3:
Notice to West Siders.
All those who live on the West Side, who desire either the Daily, Weekly, or Tri-Weekly PLAIN DEALER, can have the same left at INGHAM’s Book Store, by leaving their names with him.
 
Chronicling America
2 September 1858, Cleveland (OH) Morning Leader, pg. 3, col. 2:
The fence will be a great improvement to the West Siders’ Park.
 
Google Books
From Heaven to New York:
or, The Good Hearts and the Brown Stone Fronts
By Isaac George Reed, Jr.
New York, NY: Murray Hill Publishing Company
1876
Pg. 44:
Very properly, too; for if the West-siders mingled with the East-siders, what in Heaven’s name would become of all our “social distinctions?”
 
Google Books
9 July 1879, Puck magazine, pg. 275, col. 3:
West-siders and East-siders (of Manhattan—ed.) have all the facilities they can ask for in quick communication between their business and their homes.
 
Google Books
February 1899, Metropolitan Magazine, “New York’s Newest Aristocratic Quarter” by Gilson Willets,  pg. 140, col. 1:
The name, Upper West Side, is the invention of a New York newspaper. With fine discrimination this journal prints the social news of the city under two special heads: the one, “Society, and the other, “The Upper West Side.” After describing the dinners, drives, and dances of the Astors and the Vanderbilts, the paper draws a heavy line and then chronicles the luncheons, lap-dogs, and lemonade parties of the Upper West Side. This is certainly a great mistake on the part of the paper. To hav etheir gowns and goings-on reported as events apart from society, naturally hurts the feelings of the rich and socially ambitious Upper West-Siders.
 
OCLC WorldCat record
The Westsider.
Publisher: New York, N.Y. : Westsider Pub. Co.
Edition/Format:   Newspaper : English
Other Titles: Westsider (New York, N.Y. : 1933)
 
OCLC WorldCat record
The Westsider, vol. 2, no. 5.
Publisher: N.Y., West Side Association of Commerce, Inc. [1937]
Edition/Format:   Book : English
 
OCLC WorldCat record
West-Sider.
Author: West Side Discussion Group.
Publisher: New York, N.Y. : West Side Discussion Group, 1971-
Edition/Format:   Journal, magazine : Periodical : English
 
OCLC WorldCat record
The Westsider.
Author: Manhattan Media.
Publisher: New York [N.Y.] : Enlightment Press
Edition/Format:   Newspaper : English
Other Titles: Westsider (New York, N.Y. : 1972)
 
Manhattan Media
THE WESTSIDER
The Westsider, also available by subscription, serves residents between 60th and 125th streets, from Central Park to the banks of the Hudson. It covers a wide range of news—from politics to environmental issues—that affect readers’ everyday lives.