In 1830, had a population of 6,000 - quite large for a town so far west at the time. It had, "on the eve of the [war of 1812]" (about 1810, I guess) 1000 inhabitants; by 1818, 3,500 inhabitants(!). By 1821, the French population had dwindled to 155 families (hard to compare to absolute population numbers, but that's all I have). The French element was, however still quite significant in the 1820s, making it the center of a fairly strong Catholic element in the Mississippi valley.
Until the 1803 Louisiana Purchase, it was French territory, and as a well situated river town, it was no mere frontier outpost.
Source: (for population 1830) Wade, Urban Frontier, p 201.
For the late territorial and early state days of Missouri (a couple of years before and after 1820), Chambers, ..Benton is useful.