The horn circuit is not protected by any of the fuses in the fuse box.
Power for the horn is taken from the bussbar/junction block on the horn relay. This circuit is connected to the + side of the battery with a 10ga red wire that runs across the radiator support. It is protected by a 14ga fusible link right off the + battery terminal. This circuit feeds power to everything in the car (except the starter) so everything (not just the horn) will quit working if this fusible link is bad.
There's a 20ga black wire that connects the horn relay to the horn button. The horn button grounds this wire to activate the relay. If you temporarily jumper this wire to ground and the horn works, the problem is most likely in the horn button or a little bit of surface rust on the center hub of the steering wheel that isn't allowing the button to make a good ground.
Finally, there's a 14ga dark green wire that connects the relay to the horn. If the horn still doesn't work when you jumper the black wire to ground, try temporarily jumpering this green wire to the relay's + bussbar. If that makes the horn work then the problem is likely the relay. If not, the problem is likely a bad connection (either power or ground) at the horn or a bad horn.