Where in the milky way galaxy is castor star found?

Present estimates of the dimensions of the Milky Way galaxy place its diameter at roughly 100,000 light years.

The star "Castor" in the constellation of Gemini is about 50 light years distant from our solar system,

or roughly 0.05 percent of the distance across the galaxy.

Castor is closer to us than your average next-door neighbor.