Green’s Dictionary of Slang

1. a boom town.

1889		Idaho City (ID) World 3 Sept. 1/2: If the Custer mill starts again this fall [...] old Custer with her numerous mines of high-grade ore, will be a ‘boomer.’ [DA].
1947–53		W. Guthrie Seeds of Man (1995) 313: You ain’t a-runnin’ in none o’ them boomer town whores now.
1950		Goldin et al. DAUL 32/1: Boomer. A swiftly growing community, hence good prospect for thieves and carnival grifters.

2. (US) an enthusiast, esp. one who promotes or pushes a new enterprise, e.g. opening up a new territory or state.

1880		Illinois State Journal (Springfield) 27 May 4/1: The [...] Convention took care that the ‘unit rule’ should not be broken, as the Blaine boomers threaten to do [DA].
1888		M.D. Woodward Checkered Years (1937) 4 July 232: A Fargo boomer who said ‘’Tis the best country in God’s world’.
1903		‘Dads Wayback’ in Sun. Times (Sydney) 21 June 5/4: ‘[L]and sharks, railway wreckers, town boomers, allotment fakirs, false prophets [...] an’ bogus creeds’.
1906		A. Adams ‘In the Hands of His Friends’ in Cattle Brands 🌐 Coon Floyd’s compliments went with five cow-bells, which we always thought he rustled from a boomer’s wagon that broke down over on the Reno trail.
1915		S. Ford Torchy, Private Sec. 229: One of the boomers [...] was struck with the brilliant idea that he could make use of my peculiar talents in making known the coming glories of the new South.
1939		W. Winchell On Broadway 8 Aug. [synd. col.] Supreme Court Justice Owen Roberts may be the Repub’s dark steed. His boomers point out that he is liberal enough to satisfy the libs in the Repub party.
1940		S.J. Simonsen Among the Sourdoughs 11: It was getting pretty tough for us boomers.
1956		N. Algren Walk on the Wild Side 113: Boomers and shark already lolled the palmetto sands. ‘Makin’ any money?’ they asked instead of ‘good morning’.
2001		N. Tosches Where Dead Voices Gather (ms.) 271: Izzy had once worked for Harry Von Tilzer as a lowly boomer, a shill paid to applaud and enthuse wildly at the performance of any song published by the house of Von Tilzer.