Yes! You can visit Niagara Falls without crossing into Canada. The falls straddle the border between the United States and Canada, and the American Falls and Bridal Veil Falls are entirely within the United States.
On the American side, known as Niagara Falls, New York, there are plenty of viewpoints, parks, and attractions to enjoy the falls. Niagara Falls State Park, Cave of the Winds, and the Maid of the Mist boat tour are popular spots on the American side.
While the Canadian side offers a different perspective and additional attractions, you can still experience the beauty and grandeur of Niagara Falls without going to Canada.