Slow Town, n. — Green’s Dictionary of Slang

Slow Town n.

[? its image among hobos, or play on its role as a car manufacturer, i.e. ‘slow down’]

(US) Detroit.

1901		J. Flynt World of Graft 9: Other cities have similar nicknames. [...] Boston, ‘Bean-Town’; Detroit, ‘Slow-Town’.
1975		Indep. (Long Beach, CA) 15 Aug. 31/4: Talk to the natives in Detroit [...] or in the case of the Detroit Tigers, Slowtown.
2009		Lancaster Eagle-Gaz. (OH) 15 June 6/1: [heading] Motown or Slowtown, Detroit’s still vital to us all.