They were first made by a cast of wood craftsmen (kijiya) who were making bowls and trays. The small wooden dolls were sold to the onsen visitors as souvenirs and toys.
The craft spread in the Tohoku area, and more recently artists from around Japan started making more diverse "creative kokeshi" (shingata kokeshi). But the tradional kokeshi are still made in Tohoku and they maintain the style of each zone, which differs through color, shape, and the type of wood. The dolls in today's photo are from Kakunodate and are made of cherry tree.
EXIF info:
Nikon Df
Lens: 24-70mm F/2.8G
Focal Length: 36mm
Aperture: F/5.6
Shutter Speed: 1/200s
ISO Sensitivity: ISO 3200