I live in a wooded hilly frozen place, 3 months of summer and 9 months of poor sleddin as they say around here, (not that bad), but up until the end of May we can get freeze warnings, and I keep a woodfire going in the stove from October till May, most times. I've had chickens all this time. 3/4 an acre is what I have fenced off for them, and it could easily handle up to 50 for free range, but the most I have had is around 35. They need about 4 square ft for roosting, you would want them to cuddle and keep each other warm through the cold months, they do fine in the mid to low 30's, in their housing, you dont want drafts but you do want ventilation. On the coldest of the coldest nights, below zero days on end and nights dipping to 20 below, is a challenge. I have a big walk in cellar with cages for that purpose, but you dont want to warm them on normal winter nights, teens-30's, they do fine if they are a winter hardy breed. You can hang heater lamps, and they also make these mats in different sizes for seed starting, to put on under the shavings. When I get new chicks, I get them in May, keep them in a spot indoors with a heat lamp until they have all their feathers and can fly up to roost, and put them in the barn around the beginning of July, and they are good to go. Use a generous amount of straw and shavings on the floor, make sure they have light in the barn, (passive solar), and they will be fine. I get my chicks from two places, Murray Macmurray hatchery, and Meyers, and Hoovers, all ship good healthy chicks, MacMurrays sells good equipment. In the winter I put a kiddy pool in the barn with tube sand and wood ash mixed so they can dust themselves , as they will get lice through winter if they cannot dust themselves off. Sometimes you lose a few, but if you check on the flock once a day in the winter, and notice one or two all huddled and shivery and sleepy, they need to get warmed up, sometimes they are the ones on the end or the one that is unpopular and cannot get cozy enough, Make sure to get chicks that are labelled as winter hardy, and it should be fine.

Winter hardy breeds can survive winters just fine.

We have a 60sqft coop non insulated that houses 10 chickens just fine in USDA Hardiness Zone 5a.

you might find that chickens will refuse to walk on snow but if you clear it away enough to see some kind of ground or make a path of straw/hay, pineneedles, woodchips, etc they'll go out on that.

Winter Chicken

we live in central Florida so the cold is usually not an issue. The problem we have is predators, so we can't "free-range" them. We have 3 separate chicken runs linked together that are about 30x14 each. We let them eat the grass and weeds off 1 while we reseed the other 2. We still have to supplement with grain, but I make fodder with wheat and sunflower seeds. I ferment the seeds as well... really cuts the cost. Also, I buy meal-worms for a treat - about $50 a month. The rest of the grain runs about $55 for a 3 month supply of wheat (Tho that price is going up) and $35 for the sunflower seeds (black oil sunflower) which lasts about 3 months as well. I use cheap fast-growing grass seed to re-seed the runs - it costs maybe $2 for each re-seeding.

we also feed them veggie scraps (from our garden) and I grow a shitton of bananas and papaya. Chickens can eat every part of the banana plants and they go ape over papaya.

I live in the Rocky Mountains at about 10k feet. LOTS of snow. Long winters. I built my own insulated coop and ran power out to it for a couple heat lamps that i turn on when it is really cold. Even when it is around zero outside the coop stays about 45 degrees. I put up a large loafing shed attached to the coop that is open on one side so the chickens have somewhere without snow to walk around in the winter. Also the coop is elevated about a foot and a half off the ground. Giving them somewhere to hide from hawks and the elements. The bigest challenge is keeping their water from freezing. I recommend using rubber bowls so when it freezes you can stomp the ice out and refill. You would be suprised how hardy chickens are but i try to keep them as comfortable as reasonably possible. I know someone who keeps a flock up in Alaska. They can thrive anywhere with a little acomodation.

Northern IN here. I have a coop and fenced run, and they did great with just some extra hay on the floor during the week of -30 windchill a few weeks ago. We did keep them locked in the coop with fresh water and food, but they do great