Is there a minimum, NEC-compliant distance that an electrical outlet can be off the floor in my home?
I wasn't able to find anything that limited the height of receptacles, in fact, they can even be in the floor.


  210.52 Dwelling Unit Receptacle Outlets. 
  
  (3) Floor Receptacles. Receptacle outlets in ﬂoors shall not be counted as part of the required number of receptacle outlets unless
  located within 450 mm (18 in.) of the wall.


I think typically they're between 16 - 18", but it doesn't look like there are any hard set rules on this for general purpose receptacles (at least as far as NEC is concerned).

Mike Holt says...


  No. There is no NEC requirement on the height of wall-mounted
  receptacles in residential, commercial, or industrial facilities,
  but….


Source

He then goes on to talk about the American Disabilities Act (ADA) and other building code organizations rules.