Yes, CASES is a Scrabble word!

Letter values in Scrabble US: C 3, A 1, S 1, E 1, S 1.

Is it a valid word?

CASES is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

an occurrence of something
a special set of circumstances
a comprehensive term for any proceeding in a court of law whereby an individual seeks a legal remedy
the actual state of things
a portable container for carrying several objects
a person requiring professional services
a person who is subjected to experimental or other observational procedures; someone who is an object of investigation
a problem requiring investigation
a statement of facts and reasons used to support an argument
the quantity contained in a case
nouns or pronouns or adjectives (often marked by inflection) related in some way to other words in a sentence
a specific state of mind that is temporary
a person of a specified kind (usually with many eccentricities)
a specific size and style of type within a type family
an enveloping structure or covering enclosing an animal or plant organ or part
the housing or outer covering of something
the enclosing frame around a door or window opening
(printing) the receptacle in which a compositor has his type, which is divided into compartments for the different letters, spaces, or numbers
bed linen consisting of a cover for a pillow
a glass container used to store and display items in a shop or museum or home

Also: guinea pig, grammatical case, compositor's case, typesetter's case, pillow slip, display case.

Not playable in Scrabble US: CAUSA, CASEFUL.