A person with this number 301-{removed} what country can he or she likely be us or uk

Its likely from the US and from this area:
301 area code: map, locations covered and time zone
Not all caller ID's are accurate.

The number was for a cell phone, it was in the Westchester, MD area.

Not all of these are accurate. My son called me from Iraq on a calling card... I got an area code out of Santa Fe New Mexico on my caller ID.

and many marketing and bill collectors somehow get their caller id to show other numbers, many disconnected and others random numbers so you can't call them back