When you think of guardianship records, do you think they are only for children? Think again. The law also provided for guardianships to be established for adults in various situations. A guardianship could be for mental incapacity (unsound mind, insane and idiot were the main categories), but there were also guardianships for being a "habitual drunkard" or for old age (referred to as "aged and infirm").
Whether the guardianship was for a minor or an adult, it will be found in probate records. If the guardianship was for unsound mind or insanity, there was a separate court proceeding to prove the mental incapacity, so you'll also want to look for "insanity inquests" in court records.
As a general rule, probate cases are their own record group and are kept separate from civil cases. However, when the probate case is about the guardianship of an adult, you also need to look in civil court records. Guardianship cases normally begin with someone filing an application in probate court to be appointed guardian. However, if their intended ward is an adult, a separate case must first be filed in civil court. This civil court case is full of details that will not be found in the probate case. The intended guardian must specify why they believe the adult cannot care for themselves (whether it's because of habitual drunkenness, mental incapacity, old & infirm, etc.) and provide witnesses to support their claims. A jury then rules on the case.
NOTE: The adult ward can later file a petition to end the guardianship and have their remaining assets returned to them - if you see this notation in their probate case, don't forget to also look for that follow-up case in the civil court records.