An “East Sider” (or “Eastsider,” also lowercase “east sider” and “eastsider") is someone who inhabits the east side of a geographical area. “East-siders” was cited in print in November 1850, when it referred to Milwaukee, Wisconsin. An August 1853 citation of “east-siders” referred to Manhattan.
Similar Manhattan geographic nicknames include “West Sider,” “downtowner” and “uptowner.”
(Oxford English Dictionary)
East Sider, n.
A native or inhabitant of the East Side of a city, esp. of Manhattan’s East Side.
1861 A. C. Wheeler Chron. Milwaukee xvii. 144 The Major was a confirmed east-sider, but he took no interest in the sectional quarrel.
1880 Scribner’s Monthly Nov. 50/1 Insensibly the East-sider was set above the man of training or affairs whose team he drove.
1903 N.Y. Tribune 25 Oct., 15,000 East Siders attended the final dedication ceremonies at William H. Seward Park.
19 November 1850, Daily Free Democrat (Milwaukee, WI), pg. 2, col. 4:
ALARM.—Some “larks,” out late hallooing, screaming, and singing songs, last night, alarmed the East-siders, who started the cry of Fire, set their bells a-dinging, and ran out with their machines, to see what was to pay.
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.
27 August 1853, The Literary World, pg. 70, cols. 2-3:
CHATHAM STREET. (New York City—ed.)
It is the bread-plant of these east-siders, their manna in the wilderness.
13 September 1860, Rockford (IL) Republican, “Another Falsehood,” pg. 2, col. 6:
Let those who remember the bitterness of the fight made by the East siders (of Rockford—ed.) over the claims of Mr. Southgate, answer.
28 August 1865, Cleveland (OH) Leader, “Gala Day on the West Side,” pg. 4, col. 5:
This Mammoth Menagerie will exhibit on Tuesday on Erie Street, East Side, thus affording an opportunity to the East Siders of visiting this mammoth exhibition.
Eulogy on James W. Lingard
By Thomas Allston Brown
New York, NY: Crocker Brothers, Printers and Stationers
He studied and worked hard to please the east siders by constantly producing novelties, and, by close attention to business, made the New Bowery popular.
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
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?”
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.