I don't know what kind of music your choir sings, but you could hold it to celebrate the birthday of a composer connected to your repetoire.
I need an occasion for choir day, ideas?
Arbor Day might offer some inspiration. There are some beautiful compositions about trees and forests.
William Clayton (Governor), acting Governor of the Pennsylvania Colony in 1684-1685 (d. 1689) was born in 1632. Of course, I doubt there are any choral arrangements to cover the event.