Can users stay logged in to a specific site on my multi-site?

I have a multi-site network with the main site being the corporate site for my company and the sub-sites (set up as sub-directories) are for each of the regions that we service. Each region has the appointments calendar for that specific region on their site, so customers in that region can view that regions schedule and set an appointment. They are able to view the schedule prior to logging in, but are required to be logged in before they can schedule an appointment.
Is it possible to set it up so that when that customer returns to our site they are automatically sent back to the sub-site of the last region they scheduled an appointment? This way they don't have to go back through all of the prompts to send them to their region's sub-site each time they want to make an appointment.
Is this possible using plugins, as I am not very code savvy?