We found him in one of the structures around the Pipeline in the Arid Nexus; I'll try and find the location's name tonight.
He was in a random Hyperion ammo/cash chest on top of the building.
It appears he spawns randomly; I found him in a coop game once, then searching the area again solo
I failed to find him.
Sidenote, in coop he only counts for the single player that deal the killing blow.
Share with your buddies or farm him solo; if you seriously want to max out the challenge it'll take a long time.
I've also found him in one of the Loot Midget boxes in the Wildlife Exploitation Preserve (there's 4 of them near the place where you first try to find bloodwing, with the shielded pens).
I think he might spawn anywhere a Hyperion Loot Midget (LWT Loader, Loot Gun Loader Midget, Loot Jet Loader Midget) can spawn.
gaming.stackexchange.com/users/11920/Ben Brocka
If you have a character that is doing the " Wildlife Preservation " and the " Doctor's Orders " missions you will always have something jump out of the boxes near bloodwings first holding cell.
Eventually Jimmy Jenkins will bo one of those loot midgets.
There is no where else where you can have loot midgets every time so this place works the best.
When I finally killed Jimmy he jumped out of the first and fouth boxes so I was able to kill him twice in this room.
Having the above mentioned missions active is required.
gaming.stackexchange.com/users/36803/Logan
According to random message boards on the internet, he is located at or around Crater Lake.
gaming.stackexchange.com/users/33279/Jake
I just found him in a cardboard box in T.K.'s house.
Made me want my own little Jimmy Jenkins to hide in boxes.....
gaming.stackexchange.com/users/33645/Cody
He has a chance of spawning where "trap boxes" are.
So wherever you come across a loot midget or anything that come out of something: REMEMBER IT!
Eventually Jimmy might come out.
Anything after the wildlife reservation has the best chances!
gaming.stackexchange.com/users/33675/Nick
Jimmy Jenkins is a named variant of the "Wee Loot Loader" that can spawn randomly from Hyperion ammo crates.
As part of the Challenge Accepted achievement/trophy, you'll have to kill him at least once.
There is a "glitch" of sorts that involves having the Doctor's Orders quest and opening the crates in one particular room of the Wildlife Exploitation Preserve.
There is a high chance of getting a Loot Midget/Loader from these crates.
If you have the Creature Slaughter Dome DLC, you can spawn from the Dome's exit and repeatedly enter the game, open the boxes, and quit in order to farm him fast.
Gearbox patched this at one point and it stopped working, although I believe they reverted the patch.
It's a cheap way to farm loot loaders in Ultimate Vault Hunter Mode, which have a chance to drop very high level items, so it may get patched again in the future.
If the "glitch" has been patched, you don't have this quest anymore (or it would be a pain to get it) and/or
you don't have the DLC, you'll need to find a high concentration of Hyperion ammo crates to farm him from.
I used the part of Thousand Cuts close to the exit to the Bunker.
I've got a map detailing my route plus some helpful tips over here if that's of interest.
One note
I'll mention directly here
is that there appears to be a very low chance (possibly none?) of spawning a loot midget/loader from a crate if there are enemies around, so you'll want to clear an area before you go box-crazy.
gaming.stackexchange.com/users/13845/agent86
There is a strange challenge ("JEEEEENKINSSSSSS!!!" under "Miscellaneous") that involves killing Jimmy Jenkins. Where is he?
Where is Jimmy Jenkins?
gaming.stackexchange.com
<borderlands-2>
gaming.stackexchange.com/questions/84851
gaming.stackexchange.com/users/21177/Wolf
He has been found around the Pipeline in the Arid Nexus, in the Loot Midget boxes in the Wildlife Exploitation Preserve and near a Hyperion Loot Midget. The most common suggestion, regarding Jimmy Jenkins location, is Midget boxes.
The community lists few locations that Jimmy Jenkins can be found.