A person who lives in or who frequently goes downtown is a "downtowner." "Just like downtown" (meaning something very good and exciting) became a popular saying in the 1950s.
(Oxford English Dictionary)
downtown, down-town, adv., a., and n.
orig. U.S. and chiefly N. Amer.
A. adv. Into the town (from a more elevated suburb); down in the town. Cf. UP-TOWN adv.
1835 GRAY Lett. (1893) 55 To-day when I go down town I shall subscribe for the 'New York Observer' for you.
1883 Century Mag. XXVI. 917/1 She was down-town alone. c1909 D. H. LAWRENCE Collier's Friday Night (1934) iii. 60 Well, my duck, I looked for you downtown.
1952 S. KAUFFMANN Philanderer (1957) vi. 91 The man who had seemed a dignified young wonder on 135th Street..looked like a pompous and overweening young ass downtown.
1968 Globe & Mail (Toronto) 17 Feb. 24 (Advt.), Tickets available downtown at box office prices exclusively at Moody's in the Colonnade.
B. adj. Of, pertaining to, or situated in the lower, or more central, part of a town or city. Cf. UP-TOWN a.
1836 P. HONE Diary (1889) I. 200 The value of down-town property.
1852 Harper's Mag. V. 413/2 The down-town men..slip uneasily through the brick and mortar labyrinths of Maiden-lane. 1870 J. K. MEDBERY Men & Myst. Wall Street 67 On these securities therefore the down-town banks make call loans.
1883 H. H. KANE in Harper's Mag. Nov. 944/2 In the lobby of a down-town hotel.
1891 Congress. Rec. 28 Jan. 1906/1 The second ward of the city of New York..is what is called a down-town ward, a business ward.
C. n. The lower or business part of a town or city.
1851 H. MELVILLE Moby Dick i, Its extreme down-town is the Battery.
1905 N.Y. Even. Post 4 Mar. 5 One of the diversions of downtown yesterday was watching the sure movements of a steeplejack. 1955 R. BLESH Shining Trumpets (ed. 3) vii. 160 New Orleans' downtown is the old quarter north of Canal Street. 1968 Globe & Mail (Toronto) 13 Jan. 45/1 (Advt.), At the subway stop..19 minutes from downtown.
Hence down-towner, one who lives in or frequents the down-town part of a city.
1830 J. F. WATSON Ann. Philadelphia 244 They were the Achilles and the Patrocles of the 'downtowners'.
1887 Courier-Journal (Louisville, Ky.) 8 May 12/5 Jay Gould has set down-towners to eating snails.