Dude, where's my horse? Here is what to do if you don't remember where you left your horse or other mount.
How to Retrieve Your Missing Horses and Mounts
If you can't find your horse or other mount, you can purchase another stable from the carpenter's workshop, build it on your farm, then check on the door of the stable to see the list of mounts that are kept there. Then you can press L or R to look through all of your stables, including the one that your missing mount is assigned to. This will allow you to move that horse or mount to the stable that you just built. Just press A to select the horse or mount, then press L or R to go to the destination stable, then press A again to assign the mount to the stable. The mount will be moved instantly to the new stable. This solution may be less than ideal, but it is a guaranteed way to find your missing mounts.
Drop Your Horse Off at the Farm
Horses and mounts that are left in town will stay there until you pick them up again, but horses and mounts left on your farm will automatically return to their assigned stable the next day. To avoid losing your horse or other mounts, be sure to take them back to your farm instead of leaving them in town.