Texas Eagle (Amtrak train) St Louis to Chicago
 

Might give this a go as it's around $36 for a coach seat Vs. $150 on AA (and the time taken possibly won't be too different factoring in getting to and from the airports)

Anyway, looking at a Monday departure.

Would I expect this to be packed? A post or two somewhere else says yes

Our son went to college/grad school in St Louis and we experimented with all sorts of public transport in getting him between out house (NW suburban Chicago) and his school (in the CWE part of St Louis). We found that while flying was the most expensive alternative it was also by far the most convenient and on-time. My son took Amtrak a total of three times and he was never on time. Two of the delays were marginal (30 - 60 minutes). But one involved a freight train on their track and was several hours in delay. This was in the 2006-2014 time frame. I have read that there have been improvements recently (in the last 2 years) along with a promised increase in train speed (up to 110 mph).

We are (at most) 20 - 25 minutes from ORD and the tme for him to get from school to the airport was at most 30 minutes. So if you include a two hour check in window at STL, he was something like 4 to 4,5 hours away. The scheduled train ride was (and still is) 5.5 hours. Assuming normal check in and connection times to and from the relevant train stations, the total trip time would be something like 8 hours, at an absolute minimum

If you are going from city center to city center, the train could be very workable for you. Otherwise, depending on the distance travelled between source/destination and the relevant train station, you will likely find that flying will be more convenient but more expensive.

I want to be in the loop area of Chicago and not sure if the blue line from the airport is still having works done. Few delays and packed trains last time I went back to the airport, and the time before that, replacement buses in places.

Anyway, I changed to an evening train the day before. Supposed to get in at 10:44pm, and then up to 15 mins or so walk to my hotel, but not too fussed if it were running late.
(Would rather stay the night in Chicago to be honest than St Louis, and get up around 6am for an 8am departure.)

Flights are £200+ now, so even more of a bargain on the train.
(Did look at redemptions using BA Avios, but nothing on the day I want to travel after 10am which is too early. Next day, either early; too much for a 1h20 flight; later in the day that reduces my Chicago time)

I'll give it a shot. Either it will be an experience and a half, or work out fairly well for me.

Have taken Amtrak between PHL and NYC before and that was fine. Bit of a rush to get a seat, but got a window and the train filled up. Comfy and not that bad an experience for the $20-$25 it cost me..

I think the only real potential issue with your plan is that you never know how much the train will be delayed due to freight traffic. Amtrak uses freight railroads in most of the US outside of the Boston-NYC-PHL area, and the freight trains have priority. It's also possible the train will have an equipment problem, which anecdotally seems to be not uncommon.

But, it'll be a relatively pleasant experience with a bar car, tons more legroom than a plane, ability to get up and walk around, a power outlet at your seat, and probably wifi, as you glide through the corn fields.

The Texas Eagle is the least dependable since it comes from Texas. It will probably be late. Real late. The Abraham Lincoln service originates in Kansas City, so is relatively on time. If you take Amtrak, take the Lincoln service. Better odds.

Your post was a while ago but posting for anyone who may see this...you can check https://www.transitchicago.com on the day for the status of the Blue Line including any maintenance or shutdowns.

Anecdotally...I live in the Loop and take the Blue Line to and from ORD regularly. There hasn't been any widespread scheduled maintenance in a while. The weekend line cut with replacement shuttle buses for track replacement near Belmont was completed last spring (2023). The other major aggravation for well over a year post-COVID was the "no train departures from ORD midnight-4 AM" (replacement shuttle buses from ORD to Rosemont), but that issue was miraculously fixed during last year's mayoral election.