Inishmore in October

We were there in midsummer (early July). We had a mix of weather then: windy with some sun, windy with some rain, and windy with sun and rain mixed together. Have not been there in October but my sense is that you should expect a mix, though your mix would probably be a lot more rain and less sun. In early October you might luck out with a decent portion of sun in the mix (though don't count on it), while in late October I would expect mostly rain most of the time.

It's the western edge of northern Europe, fully exposed to the brunt of the North Atlantic...wind and rain is mostly what they get, except during the brief summer. It's a lovely place, and I bet there would be few tourists to share it with in October. But if you do go then, definitely bring appropriate (serious) rain gear, and the expectation that it could be very wet the whole time you are there.

Ok that is what we were thinking ~ thank you.

October is historically one of the rainier months for NW Ireland. Add to that the short Autumn days and seasonally cooler temps and the prospect isn't particularly good. Still, you could get lucky with a few pleasant days strung together. Best advice would be to wait until you're there (in Galway I assume) and check the near term forecast - the ferry isn't going to sell out so you can literally wait until a few hours before departure before making up your mind.
Since the ferry can be a rough ride in any season if sea states are up an alternative would be to fly. Can view schedules and pricing here: https://aerarannislands.ie/

Thanks so much.

Do you know if the mini van tours need to be booked ahead? Or maybe even just the day before?

The island gets a steady stream of tourists in the summer months -- though it is still a pretty small, low-key place. That is, the tourist services/infrastructure that they do have is fairly limited, so don't expect lots of options. Outside of their "peak" summer season (a relative term), I bet tourist numbers drop way, way off as the weather turns ugly. I would probably be more worried that mini van tours (or any other tourist services) are shut down completely for the off season, than I would be worried about not getting a seat on a sold-out tour in October.

Find the tour van people, shoot them an email and ask if they're open at all in October and if yes, let them know you're coming when you have your plan finalized (otherwise they may not answer the phone when you show up). No worries about "overtourism" there in October.

If you do go, absolutely do take the flight if you can, rather than the ferry. It's a very short flight (less than 10 minutes from engine start to shutdown) and buys you hours more of usable time on the island (the plane is tiny and they fly at treetop level...it's quite a ride).

As David says, you won't have to worry about any crowds in October.
There will be mini-vans and pony traps lined up on the pier when the ferry arrives. All you need to do is walk a few yards and pick one that looks good to you - no need to book ahead.
Don't know how it works from the little airport but would guess that there will be a lineup there to meet you as well.

Thanks so much!

When we landed at the airport, they (the Aer Arann folks) had a van waiting for us; all the passengers (other than locals who were walking/already had rides) piled in, they drove around and dropped everyone off where they wanted, us at our B&B. As easy as could be. I don't recall seeing any other vans, certainly no horse-drawn carts, there. We drove right through the main "town" (near the ferry dock) so I'm sure you could just hop out there and pick your pony from the ferry line.

Hint: When you check in for your flight on Aer Arann, request the front row, right seat (that's the co-pilot's seat). Best views in the world from there if they seat you there (just don't touch the flight controls...)

Great tip on the seat!