I'm so sorry to hear of your lost letter. I'm a little confused about the dates. You stated it was processed through Chicago on Aug. 9. However, the USPS tracking information provides a date of Feb. 5. If it was that recent, the odds of finding it are much higher. If nearly seven months have passed, though, it may be impossible to find. Nevertheless, should you care to continue to try, I can offer you a few avenues you may not have thought of, if you're interested.
For example, it is possible to find address and local phone numbers for the post offices in Akron and Aurora.There are several mail sort facilities near zip code 60666 in Chicago that also have local phone numbers. Of course, there's no guarantee an actual person will answer those local numbers either, but at least they're not the main 1-800 number so the odds are a bit higher.
Then there is the Mail Recovery Center (formerly known as the dead letter office) with two locations: Atlanta, GA and St. Paul MN. There is a procedure you can follow to initiate a search for lost items, and I can include instructions on how to proceed. Letters are retained for only three months, parcels for six months, so it may already be too late if the Aug. 9 date is correct. If not, there's a chance. It's another possibility that might be worth pursuing.
Finally, it's also possible your item was held up in Irish customs. Apparently the Irish Customs has been unusually active for the past year or so in retaining international mail, causing it to be held up for weeks or months. There is a form on the Irish post site allowing you to submit a request for a search of their archives by inputting the tracking number. They do provide tracking of incoming international mail, and state they will email you either information on the location or disposition of the mail, or that they were unable to find it.
Please let me know whether you'd like to see any of this information. I won't post it as an answer unless you give the go-ahead as it's not definitive information on the location of your lost mail.
In any case, best wishes and sympathies on a frustrating situation.