NGS Style Manual‎ > ‎- N -‎ > ‎

north, northern

As a compass direction, north and northern are not capitalized:
            He lived north of the city.
            He lived in the northern suburbs.

Capitalize each term when it is used as a proper name or as part of a proper name, and if the region is widely known:
            The Civil War pitted the North against the South.
            He lived in Northern Virginia.


U.S. context
North
North Jersey
Northerner
northern states
Northeast
Northwest
Northeasterner
north-central states
Northern Virginia 
Northern California
north, northern


Other contexts
northeast, northwest
North Pole, but the pole
North Africa
northern Europe
Northern Hemisphere, the hemisphere
far north, the north (Arctic region)
North Atlantic, North Pacific
true north
Northeast, or Dongbei (Manchuria)
 
See also pole, polar, south, southern.