If you don't want to kill it, trap and release it. They are easy to trap with a havahart trap baited with peanut butter. Be sure to drive it far when you release it, or it will come right back.

What damage it[they!!] might do depends on what you raise. They love to eat on sweerpotato 'tubers' for example.

Your best hope is for a garter snake to move in your garden to "take care of the problem" if you should have a problem.

Cat? Or, if you're a dog person, a Jack Russell Terrier. But, take my word for it, a cat is easier.

There is a live trap called the Tin Cat that works quite well. We've used it when our cats get too lazy or old. The mouse goes in, can't get out, and the lid pops open for easy release. I'm not affiliated with the company in the link, just wanted to show a picture of the trap. You can probably get a better price elsewhere. We bought ours at a feed store many years ago.

Here is a link that might be useful: tin cat

If there is one, there may be 100. Do this, if you have crumbly soil: stick your finger in the soil, first in the middle of the bed(s), to feel what solid soil feels like, then 1 to 2 inches from the bed wall. If you have an invasion, you should be able to feel tunnels running parallel to the walls. Then you will become a poison person. If I find them, I use the finger hole to pour a bit of rat poison, then close.

go to the pet store and buy a couple of corn snakes and release them into the garden. They like mice!

I just put regular mouse traps in my yard and kill the mice. Normally I try to be humane, but my land borders two large parks (not sure why two parks are right next to each other, but they are) and so I have a lot of wild life in my city home. The mice try to live in my garage during the winter. One bedded down in my scooter helmet. I am still digging sunflower seeds out of it! A mouse trap and peanut butter or banana flavored laffy taffy does the trick.

They could be voles, which look like furry, short-tailed mice, breed prolifically, and love to eat garden produce. I second the mousetrap suggestion. You will kill it, but at least you're not dropping it off to invade someone else's garden.

Rat (or other) poison can kill the animal's predators. Hawks, owls, cats, can all be made very sick or killed by eating a poisoned animal. Children might eat the poison accidentally, too. I'd eschew it.

There isn't such thing as "one mouse," just so you know. Mice aren't a problem unless they are inside your house, or unless you are a corn/grain farmer. Please don't poison! My Beagle ended up in the ER because she ate a dead poisoned vole - very expensive. If you are determined to get rid of this mouse, you can buy "glue traps" at the hardware store. Basically a flat tray filled with super glue. Place it where you saw the mouse run, and it will be trapped. I find them cruel, but I'm told a mouse will die of dehydration in 24 hours. Personally, I try to live WITH nature!

I heard that bounce sheets work indoors for some people. My old neighbor said they worked for him. I don't know if they work outside, but you could try them. They've been working for me so far with mosquitos. And if you find out where they live, you could put one in there instead of poison.

In many states, including my own (WI), it is against the law to poison mice, voles, rats, and other small rodents. The number one reason for this is because the poison also kills the predators. Even if it isn't illegal in your state, it's not a good idea. Get a mouse trap, much safer for the predators.

I've had voles (field mice) chew on every potato tuber that grew under hay mulch except 1, in a potato patch of nearly 1,000 square feet! I no longer grow potatoes under mulch.

They eat ripe tomatoes. Voles eat the ends off green beans. They burrow up, under pumpkins, squash, and my beautiful melons! Once inside, they eat the seeds and sometimes, nothing else.

I've had seedlings chewed off at the soil that I have blamed on voles. And, sprouting corn seed has been dug up, sometimes repeatedly!

The old-fashioned Victor traps, baited with a raisin dipped in peanut butter work better than most anything. Tuck it in where a bird won't get to it.

I agree completely with the Crazybeaglelady ~ There isn't such thing as "one mouse." Nope, you have a colony. Your garden environment benefits them or you wouldn't have seen the one. Voles are a huge problem in orchards and with no-till agriculture. "A meadow vole can eat nearly its own weight
daily," according to Rutgers University. Since they weigh up to 3 ounces, 6 voles in your garden will eat a pound of some kind of food, every day.

Moving them won't do anyone any good. In the UK, they have been found to attack and eat frogs. A strange vole will probably be attacked by other voles.

digitSteve

If it's a vole, you'll already see damage. If it's a mouse, as crazybeaglelady says, it may be harmless. I've had very little to no garden damage from mice, and huge problems with voles.

I eventually had to buy some heavy-duty stainless-steel mesh and trench it in deeply around the whole garden. The voles dug under and bit through the hardware cloth I used for my first effort.

Last year and the yeay before that I, had a lot of rat problem.
I searched the net and fought them in more than just one way:

-- regular rat traps
-- live rat/rabbit trap(Made myself)
-- commercial rat baits
-- home made rat baits

This yer I started the program. I had some commercial baits from last year.
I kept puting one cube every night. Next morning it was gone.
Another one >>> gone: Another one >>> gone. Finally, the last one was half eaten and I think it is still there.
In addition to other various methods, last year, I live-trapped close to 20 of them, some big fat pregnant, maybe.

Like Dave said, their favorites are corn, beans, peas, sunflower seeds.High protein stuff.
They also munched on melons, chewed cucumber vines.

Now that I am reminded of them, I will activate more plans again to get them:

NOTE: if using regular traps, PLEASE put them inside a box or something.
I feel guilty causing death to the birds, that are beautiful and harmless.