Welcome to RTA!
Niagara Falls in the winter -- Here's the official site for the state park USA side. While the falls are open year-round, weather can be an issue. Cave of the Winds and Maid of the Mist, two main attractions, are closed by mid-to-late October. Fireworks only go in the summer months. Illumination of the falls at night goes year-round, but the hours vary of course.
Donna