Saloons, steamboats, and soldiers.
When it comes to cultural representations of poker as it was played in the 1800s, the majority of portrayals of the game present it either as (1) a favorite recreation in drinking establishments; (2) a way to pass the time (or line the pockets) for travelers aboard early river paddle steamers; or (3) a preferred activity among those serving in the military, including the many who represented both the Union and the Confederacy during the Civil War.
Such is the case for both contemporary accounts of 19th-century poker and for the many attempts to recreate such scenes later, including decades' worth of cinematic "horse operas" that routinely placed an ongoing poker game in every saloon ever imagined.