Свифт 5.0

let paths = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)
let documentsDirectory = paths[0]
let docURL = URL(string: documentsDirectory)!
let dataPath = docURL.appendingPathComponent("MyFolder")
if !FileManager.default.fileExists(atPath: dataPath.path) {
    do {
        try FileManager.default.createDirectory(atPath: dataPath.path, withIntermediateDirectories: true, attributes: nil)
    } catch {
        print(error.localizedDescription)
    }
}

Свифт 4.0

let paths = NSSearchPathForDirectoriesInDomains(FileManager.SearchPathDirectory.documentDirectory, FileManager.SearchPathDomainMask.userDomainMask, true)
let documentsDirectory: AnyObject = paths[0] as AnyObject
let dataPath = documentsDirectory.appendingPathComponent("MyFolder")!
    
do {
    try FileManager.default.createDirectory(atPath: dataPath.absoluteString, withIntermediateDirectories: false, attributes: nil)
} catch let error as NSError {
    print(error.localizedDescription)
}

Свифт 3.0

let paths = NSSearchPathForDirectoriesInDomains(FileManager.SearchPathDirectory.documentDirectory, FileManager.SearchPathDomainMask.userDomainMask, true)
let documentsDirectory: AnyObject = paths[0]
let dataPath = documentsDirectory.appendingPathComponent("MyFolder")!
        
do {
    try FileManager.default.createDirectory(atPath: dataPath.absoluteString, withIntermediateDirectories: false, attributes: nil)
} catch let error as NSError {
    print(error.localizedDescription)
}

Свифт 2.1

Вы можете создать каталог, используя метод ниже:

let paths = NSSearchPathForDirectoriesInDomains(NSSearchPathDirectory.DocumentDirectory, NSSearchPathDomainMask.UserDomainMask, true)
let documentsDirectory: AnyObject = paths[0]
let dataPath = documentsDirectory.stringByAppendingPathComponent("MyFolder")

do {
    try NSFileManager.defaultManager().createDirectoryAtPath(dataPath, withIntermediateDirectories: false, attributes: nil)
} catch let error as NSError {
    print(error.localizedDescription)
}

Ни один из ответов @Kampai и @Crashalot не помог мне.

.absoluteString создает URL-адрес с префиксом file:// и вызывает исключение при создании каталога. Вместо этого я использовал метод .path.

Фиксированный код для Swift 3

let documentsDirectory = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
let dataPath = documentsDirectory.appendingPathComponent("MyFolder")

do {
    try FileManager.default.createDirectory(atPath: dataPath.path, withIntermediateDirectories: true, attributes: nil)
} catch let error as NSError {
    print("Error creating directory: \(error.localizedDescription)")
}

Принятый ответ больше не компилируется, так как строка с appendingPathComponent выдает ошибку.

Вот версия Swift 3, которая компилируется:

fileprivate func createDir(dirName: String) {
    let documentsDirectory = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0]
    let dataPath = documentsDirectory.appendingPathComponent(dirName)

    do {
        try FileManager.default.createDirectory(atPath: dataPath.absoluteString, withIntermediateDirectories: false, attributes: nil)
    } catch let error as NSError {
        printError("Error creating directory: \(error.localizedDescription)")
    }
}

Свифт 4:

NSSearchPathForDirectoriesInDomains возвращает массив строк, а не URL-адресов.

appendingPathComponent to string приводит к сбою приложения с сообщением -[NSPathStore2 URLByAppendingPathComponent:]: нераспознанный селектор отправлен экземпляру

Вот версия Swift 4, которая компилируется:

    let paths = NSSearchPathForDirectoriesInDomains(FileManager.SearchPathDirectory.documentDirectory, FileManager.SearchPathDomainMask.userDomainMask, true)
    if let pathURL = URL.init(string: paths[0]) {
        let dataURL = pathURL.appendingPathComponent("MyFolder")
        do {
            try FileManager.default.createDirectory(atPath: dataURL.absoluteString, withIntermediateDirectories: true, attributes: nil)
        } catch let error as NSError {
            print(error.localizedDescription);
        }
    }
    else {
        print("Error in getting path URL");
    }

Свифт 4

// DB Directory and Path
lazy var applicationDocumentsDirectory: URL = {

    let urls = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)
    let documentDirectoryURL = urls[urls.count - 1] as URL
    let dbDirectoryURL = documentDirectoryURL.appendingPathComponent("DB")

    if FileManager.default.fileExists(atPath: dbDirectoryURL.path) == false{
        do{
            try FileManager.default.createDirectory(at: dbDirectoryURL, withIntermediateDirectories: false, attributes: nil)
        }catch{
        }
    }
    return dbDirectoryURL
}()

Свифт 5

guard let path = NSSearchPathForDirectoriesInDomains(FileManager.SearchPathDirectory.documentDirectory, FileManager.SearchPathDomainMask.userDomainMask, true).first else { return }
    if let pathURL = URL.init(string: path) {
        let dataURL = pathURL.appendingPathComponent("MyFolderName")
        do {
            try FileManager.default.createDirectory(atPath: dataURL.absoluteString, withIntermediateDirectories: true, attributes: nil)
        } catch let error as NSError {
            print(error.localizedDescription);
        }
    }
    else {
        print("Error in URL path");
    }

Более простое решение:

"~/Desktop/demo".expand.createDir()//Now you have a folder named demo on your desk

extension String{
    func createDir(_ path:String){
        do {
            try FileManager.default.createDirectory(atPath: path, withIntermediateDirectories: true, attributes: nil)
        } catch let error as NSError {
            NSLog("Unable to create directory \(error.debugDescription)")
        }
    }
    var expand:String {return NSString(string: self).expandingTildeInPath}
}

Для других разработчиков я оставлю это здесь, так как это может помочь кому-то вроде меня найти способ выяснить, где создается папка.

let paths = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true) as NSArray
let documentsDir = paths.firstObject as String
println("Path to the Documents directory\n\(documentsDir)")