Is Park a first name or a last name?

Park is a family name (last name). It is mostly a family name in South Korea and the United States.

Park is the third most common Korean family name (also spelled Bak or Pak), written first in Korean order.

How to address someone called Park

South Korea. Park is a family name and is usually written first. Write Dear Mr. Park or Dear Ms. Park, or use the full name if you cannot tell which title fits.
United States. Park is a family name, usually written last. Write Dear Mr. Park or Dear Ms. Park.

Not sure which part of a full name is which? Check the full name with the country where the person is based.

People recorded in Wikidata who carry Park as a family name or as a given name, by country of citizenship (3,027 in total).

Country	As family name	As given name	Family name share
South Korea	2,602	2	100%
United States	150	23	87%
North Korea	87	0	100%
United Kingdom	46	2	96%
Canada	31	2	94%
Australia	17	2	89%
New Zealand	15	0	100%
Estonia	8	0	100%
China	7	0	100%
Japan	6	0	100%

Wikidata covers notable people, so counts show how the name is used, not how many people carry it.

As a surname: about 106,696 people in the 2010 census, rank 289 among US surnames.
As a first name: 614 babies born between 1950 and 2017.

More on this naming tradition: How Korean names work.