How to get more settlers in my settlements in Fallout 4?
Solution 1:
To answer your actual question, settlements DO grow slowly. If you are hanging around sanctuary, waiting for people to show up, you will be waiting for awhile. To do missions and side quests. When you return to rest, drop your scrap, etc. It will have grown.
Solution 2:
The above answer is a bit misleading. As of 27NOV2015 Fallout 4 unpatched, Sanctuary Hills does not grow quickly regardless of doing missions, sleeping etc. Other settlements with similar amounts of resources grow much more quickly. It is not clear why this is the case. It's a little bit annoying, but the workaround at present is to use the satellite settlements as feeders for Sanctuary Hills. Select excess settlers in those locations via the workshop mode (hold V down until it appears in the settlement radius) then target an excess settler and select "R" to "Move" him to a different settlement. Select "Sanctuary Hills" when the locations sub menu pops up.
Solution 3:
You have to build multiple stores and set up supply routes. These two additions changed my populations from a measly 0-9 people to a whopping 20+ settlers and 60%-80% happiness. (Originally I only had defences, electricity and beds on green with little success) My Starlight Drivein now has 36 settlers (no joke, no typo) Starlight Drivein is my "business only", settlement with a lot of shops and supply routes from farms going to it .
This was done on the PS4 so there are no console commands. I also never use cheats or exploits. My charisma is maxed out. (Supposedly the population is 10+ charisma points, so if you have 4 charisma you can have 14 pop max) I don't know about that since a few of my settlements have reached 30-36 pop.
P.S remove tv's from all settlements and place all beds on player made surfaces or they won't be read by the game when you leave. Tv's have a bug
Solution 4:
Limits: Maximum number of settlers per settlement is 10 + charisma (max 11, 10 natural plus bobblehead).
Fast enlargement: 1) Poach. Go to other settlements, go into construction mode, and select "Move" in a settler to move them to the settlement you are trying to max out.
2) Build Automatrons (DLC needed). By doing this you can exceed the settler limit arbitrarily as you can always build more. Ideally do this once your settlement is maxed out in humans at 21. I max out settlements with humans by poaching, then build maxed out Sentrybots (hydraulic frame armor, heaviest weapons, Tesla coils, Assaultron laser heads) and assign them as Provisioner's on trade routes to every other available settlement. Because of the firepower these pack, it will keep effectively the entire Commonwealth pacified because no matter where the raiders spawn, there is bound to be at least a few of your Sentrybot terminator provisioners in perception range to annihilate them before they know what hit them.
Note: you need beds/food/water to match your population even if some are Automatrons.
3) Send recruitable followers to a settlement. When dismissing the followers you can always send them to any settlement t of your choosing, even if it is full. You can then assign them to farming, but don't assign them to shops as they will bever respond with a barter dialogue option. Same for Jezebel, she is also only useful for a farming assignment. The main reason why you might want to assign followers to shops and explicitly assign them beds is because that makes it easier to find them whenever you fast travel in.
I have used all of the above the get Sanctuary hills up to well over 40 settlers.