Yes, SILESIA is a Scrabble word!

Letter values in Scrabble US: S 1, I 1, L 1, E 1, S 1, I 1, A 1.

Is it a valid word?

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

a region of central Europe rich in deposits of coal and iron ore; annexed by Prussia in 1742 but now largely in Poland
a sturdy twill-weave cotton fabric; used for pockets and linings

Not playable in Scrabble US: SLASK, SLEZSKO, SCHLESIEN.