WARNING: Town mods may lower your frames, this is the down side to town mods. Using these mods will more than likely cause a drop in frames.
Mods that replace the mesh of generic farm houses:
Northern Vanilla Farmhouses: https://www.nexusmods.com/skyrimspecialedition/mods/91311
This is a must have mods. As stated it replaces the generic farm houses with a more Cities of the North friendly mesh.
The big town mod:
JK's Skyrim: https://www.nexusmods.com/skyrimspecialedition/mods/6289
This mod overhauls all cities and towns in the game with lots of clutter and sometimes new shops/npcs. This WILL have a impact on your frames. If this isn't for you try these two:
Dawn of Skyrim: https://www.nexusmods.com/skyrimspecialedition/mods/9074 (slightly less demanding than JKs.)
Spaghetti's Cities - AIO: https://www.nexusmods.com/skyrimspecialedition/mods/84735 (VERY less demanding over JKs.)
Mods that add to already existing towns and cities:
Capital Windhelm Expansion: https://www.nexusmods.com/skyrimspecialedition/mods/42990
A overhaul of the city of Windhelm, adding new buildings, areas, npcs and shop.
Capital Whiterun Expansion: https://www.nexusmods.com/skyrimspecialedition/mods/37982
The best Whiterun overhaul at the moment. New areas, npcs, buildings and quests. This guide suggests the Exterior Compatibility Version.
Windhelm Lighthouse SSE: https://www.nexusmods.com/skyrimspecialedition/mods/22315
Not really a town mod, nor is it a must have. It's just a nice little immersion building mod.
Cities of the North - Dawnstar: https://www.nexusmods.com/skyrimspecialedition/mods/28952
A new set of unique buildings for the capital of the Pale.
Cities of the North - Morthal: https://www.nexusmods.com/skyrimspecialedition/mods/34168
A new set of unique buildings for the capital of Hjaalmarch.
Cities of the North - Winterhold: https://www.nexusmods.com/skyrimspecialedition/mods/40088
A new set of unique buildings for the capital of Winterhold.
Cities of the North - Falkreath: https://www.nexusmods.com/skyrimspecialedition/mods/56731
A new set of unique buildings for the capital of Falkreath.
Solitude Docks Updated: https://www.nexusmods.com/skyrimspecialedition/mods/33777
The best Solitude Docks mod.
SKY CITY - Markarth Rising: https://www.nexusmods.com/skyrimspecialedition/mods/22482
Adds more clutter and even shops upwards the mountain Markarth is built upon.
Stonehills: https://www.nexusmods.com/skyrimspecialedition/mods/76508
Overhauls Stonehills to make it more unique.
JK's Whiterun Outskirts: https://www.nexusmods.com/skyrimspecialedition/mods/78351
An overhaul of the exterior of Whiterun.
JKs Windhelm Outskirts: https://www.nexusmods.com/skyrimspecialedition/mods/86975
Overhauls the exterior to the city of Windhelm with clutter.
Spaghetti's Towns - Kynesgrove: https://www.nexusmods.com/skyrimspecialedition/mods/88352
A small vanilla+ overhaul for the very small "town" Kynesgrove. Better still is that it's esl'd.
Spaghetti's Solstheim - Raven Rock: https://www.nexusmods.com/skyrimspecialedition/mods/90303
Lightweight overhaul of Solstheim. Esl'd for your convenience.
Spaghetti's Solstheim - Tel Mithryn: https://www.nexusmods.com/skyrimspecialedition/mods/90779
Small Tel Mithryn overhaul, esl'd ofcourse.
Spaghetti's Towns - Old Hroldan: https://www.nexusmods.com/skyrimspecialedition/mods/88790
Yet another Spaghetti town, I think you get the jist. Esl'd ofcourse.
Karthwasten Mod: https://www.nexusmods.com/skyrimspecialedition/mods/34200
Axis1211 is a town modder who makes the smaller little farms and mines into comfy little hamlets. Now he's done a few, but I'm gonna focus on the ones that expand vanilla locations. Like this one. Oh and don't forget you'll need his resources mod. (https://www.nexusmods.com/skyrimspecialedition/mods/47792)
Skaal Village Overhaul: https://www.nexusmods.com/skyrimspecialedition/mods/53733
Yes, I know, >elianora, plus its a little silly for stone buildings in such a frigid region, but hey I like it. You can skip this one if you want, for whatever reason that may be.
Mods that add new towns:
Helsmyrr: https://mega.nz/#!t3wEjKJB!tgDTEhWWJszJG8_NJAdkps7ot_WTqov2RKKAkbjOPFA
Adds a very comfy town in the Rift.
Granite Hill Village: https://www.nexusmods.com/skyrimspecialedition/mods/58335
Adds a comfy little village between Fort Sunguard, Bloated Man's Grotto and Falkreath Hold. Small but lively.
Reich Corigate: https://www.nexusmods.com/skyrimspecialedition/mods/58214
Another small, but comfy, village. This time located in the Rift by Treva's Watch.
Granitehall: https://www.nexusmods.com/skyrimspecialedition/mods/57180
Yet another small and comfy village located between Dustman's Cairn and Silent Moons Camp.
Amber Guard: https://www.nexusmods.com/skyrimspecialedition/mods/55564
This mod adds a little village near Karthwasten and Broken Tower Redoubt.
Sunthgat: https://www.nexusmods.com/skyrimspecialedition/mods/55343
Really small village but it's comfy.
Laintar Dale: https://www.nexusmods.com/skyrimspecialedition/mods/75768
Adds a village north of Yngol Barrow.
Amol Village: https://www.nexusmods.com/skyrimspecialedition/mods/75264
Adds a small settlement near Fort Amol.
Iggath: https://www.nexusmods.com/skyrimspecialedition/mods/75157
Adds a small settlement east of Whiterun. (Conflicts with Ryn's Whiterun Outskirts but my buddy Maze made a patch: https://cdn.discordapp.com/attachments/782227317576695808/1035335904946032670/Iggath-RynWhiterun.7z)
Lainalten: https://www.nexusmods.com/skyrimspecialedition/mods/61422
Adds a village between Rorikstead and Dragonbridge, right before Robber's Gorge.
Oakwood: https://www.nexusmods.com/skyrimspecialedition/mods/61007
My favorite town mod, adds a comfy little place between Falkreath and Riverwood.
Dunpar Wall: https://www.nexusmods.com/skyrimspecialedition/mods/60728
Adds a village at the crossing between Fort Dunstad, Fort Fellhammer and Dawnstar.
JK's Riften Outskirts: https://www.nexusmods.com/skyrimspecialedition/mods/90864
Adds clutter to the outside of Riften, making it feel much more like a proper city.
Quest mods that add towns:
Moon and Star: https://www.nexusmods.com/skyrimspecialedition/mods/4301
Adds a small dunmer village that has its own quests and a shop.
Helgen Reborn: https://www.nexusmods.com/skyrimspecialedition/mods/5673
Rebuild Helgen.
Mods suggested by anons (I don't use these but am told they're good.):
Markarth Outskirts: https://www.nexusmods.com/skyrimspecialedition/mods/70213
Complete overhaul of Markarth Outskirts.