Armadillo's train station was established at some point prior to 1898. It is part of the rail network of the South Western Railroad Company.
Events of Red Dead Online
In 1898, the station's post office is still in operation and can be used by the player.
Events of Red Dead Redemption 2
When visiting Armadillo in 1907, the post office is out of order and locals infected with cholera can be seen using it as shelter.
Events of Red Dead Redemption
During the events of the first game, the town has recovered from the previous epidemics and the train station is back in operation. However, the player can only use it to pay off his bounties.