Divorce records are public records in most States. However, the Idaho Dept of Health and Welfare: http://healthandwelfare.idaho.gov/?TabId=82
Says: Birth certificates are legally confidential in Idaho for 100 years. Death, stillbirth, marriage, and divorce certificates are legally confidential in Idaho for 50 years. Because of that law, the Court Clerk for the Idaho County District Court might not be able to help you without proof of identity.
You identified you don't need a certificate, just the date. Eventually you may have to provide not only the date, but the place of the divorce decree. (If this information is needed for a job, government security clearance...you will be asked to identify the date and WHERE).
So, I'm having to assuming the following: You did not initiate the action as "Petitioner." You may have been the "Respondent," receiving documents to sign for this action. You probably didn't have an attorney. If you did not receive documents to sign, or have to appear in court, you may have become divorced in absence (Indicating the court could not locate you and you were considered as having abandoned the marriage).
---OR, you may not have been divorced. If you were young and just assumed the former spouse had done it, then you might get a shock later.
You identified looking in Idaho County for the divorce. However, the legal action did not have to take place in Idaho County. If your former wife had moved to another county, she "could" have filed in that county. Or just for convenience or savings, went to another place. A divorce action does NOT have to be completed in the county of marriage... or even in the same State.
So, your own memory of events will have to be tested first. Remember WHEN and where you were married. Do you know/remember if your wife stayed in that area? When was the last time you were with your spouse as husband and wife, and where was she? When do you believe you separated? When and where do you believe she may have filed? Is there enough satisfaction in your own mind to strongly believe she filed and a divorce decree was issued? Were there any children? If so, did you have support payments to them? Were you to pay support to your wife? If there WAS support, when did it end?
Based on those questions, are you satisfied in your own mind there was a decree issued in Idaho County? If you don't know, read the next paragraph below. In most other States, a divorce/dissolution is filed in the County Superior Court. Some are in the Civil Division, some are in the Family Court Division.
Basically to solve the questions, I would recommend obtaining an official copy of your certificate. Print off the request form from: http://healthandwelfare.idaho.gov/?TabId=82
Send them the proof of acceptable identification. Send them a money order or check for $13.00. Once you receive the information back in the US Mail, save it for the next time you need proof. All the peace of mind for only $13.00.