Is Jena a first name or a last name?

Jena is both: a family name in some places and a given name in others. It is mostly a family name in India; mostly a given name in the United States.

How to address someone called Jena

India. Jena is a family name, usually written last. Write Dear Mr. Jena or Dear Ms. Jena.
United States. Jena is a given name. Hi Jena on first-name terms; formally, Mr. or Ms. goes with the family name, not with Jena.

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 Jena as a family name or as a given name, by country of citizenship (177 in total).

Country	As family name	As given name	Family name share
India	161	0	100%
United States	2	9	18%

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

As a surname: about 337 people in the 2010 census, rank 59,901 among US surnames.
As a first name: 12,836 babies born between 1950 and 2017, 100% of them girls.

More on this naming tradition: How Indian names work.