I mistakenly deleted an album. How do I get it back?

If the deletion of the album was your last action in iPhoto, try ⌘Z to undo this action.

Otherwise you can only restore the iPhoto Library from your most current backup to restore the album.

is there a recently deleted or trash folder?

iPhoto has a Trash bin, yes. If you not emptied the Trash, you can use "put Back" to restore the album.

Select the album in the trash,ctrl click it, and use "put Back".