I want to take a train from Innsbruck to Hallstatt in mid-September, What is the best rail company to check? Do I need to reserve the tickets in advance?
https://www.oebb.at/en/
The only train company that runs trains to Hallstatt.
No need for reservations. You may be able to get a discount with a nonrefundable, train specific ticket.
For express trains a seat reservation is recommended.
There are two train routes from Innsbruck to Hallstatt:
(1) Innsbruck - Salzburg - Attnang-Puchheim - (train change) - Hallstatt (travel time about 4+ hours)
(2) Innsbruck - Stainach-Irdning - (train change) - Hallstatt (travel time about 6+ hours)
Route #1 is the northern route, #2 is the southern, much more scenic route.
Note:
Because of track repairs after a landslide due to torrent rain route #2 will be fully operational effective May 11th, 2024. Until then along a short section there is a rail replacement service by bus.