(Oxford English Dictionary)
a. upper ten, the upper classes; the aristocracy. colloq. Orig. (U.S.) upper ten thousand.
(a) 1844 N. P. WILLIS in Even. Mirror (N.Y.) 11 Nov. 2/1 At present there is no distinction among the upper ten thousand of the city. 1861 LEVER One of Them xix. 149 The Peerage,..the bulky volume that records the alliances and the ages of the 'upper ten thousand'.
(b) 1846 A. J. H. DUGANNE Daguerreotype Miniature 20 Major Peyton Florence was held in great reverence by the 'upper ten'. 1848 BARTLETT Dict. Amer. 370 The upper ten thousand, and contracted, the upper ten,..the upper circles of our large cities. 1860 W. H. RUSSELL Diary in India I. 119 Petty jealousy and 'caste' reigned in the Residency; the 'upper ten' with stoical grandeur would die the 'upper ten'.
transf. 1879 JEFFERIES Wild Life 160 Neither is he [sc. the robin] a favourite with the upper class of cottagersfor there is an 'upper ten' even among cottagers.
b. Hence upper-tendom = upper ten. Chiefly U.S.
1848 F. A. BUCK Yankee Trader in Gold Rush (1930) 13, I suppose you and those other families left out constitute an Upper Ten-dom, in the place. 1855 Doesticks xvi. 131, I did go to a ball for the benefit of the poora two-dollar commingling of upper-tendom with lower-twentydom.
11 January 1845, Spirit of the Times, pg. 552:
...shaking the musical nerves of the "upper ten thousand" and frightening aspiring juveniles out of a year's growth.
25 January 1845, Broadway Journal, pg. 59:
But, whether it be true or not, there cannot be a doubt that the absence of Pico and Borghese will prove a terrible blow to the amusement of the "Upper Ten Thousand."
25 January 1845, Workingman's Advocate, pg. 3:
A Fiddler comes from Europe; is puffed by the papers; reaps rich harvests from our mushroom nobility and codfish aristocracy, "the upper ten thousand;"...