I've updated list of IPVanish servers as there were some changes, but the reason the list stops at St. Louis is because alphabetically that's the location of the last US server that IP Vanish provides. Just because you're near to a large metropolitan area it doesn't imply that there will be a server located there. You can see the list of servers on their website.
Technically, Washington is the last in the list of servers. It appears in the official IPVanish app, but not the addon. The server list stops at Washington not St Louis. I understand there won’t be one in every city, but there are several servers in Washington.