Yellowstone National Park is 3,472 square miles according to YNP facts. 

Yes, Yellowstone NP is a large park, and while it is not the largest US National Park, it is big enough that I recommend staying in multiple locations of the park (or just outside of the park) in order to maximize animal viewing and photography while minimizing driving when dark.  Many animals are active at dawn and dusk, but driving in the dark can be very dangerous because animals large and small may run across or down the roads, so please minimize driving at night for your safety and for that of the many animals.  Even though I have driven many miles in Maine and New Hampshire keeping a careful eye out for moose, I consider the bison in Yellowstone NP to be the black-holes of light.  They often cross or walk/run the roads and are very difficult to spot at night. Even when walking in six inches of snow, they just suck up headlights.  Staying in multiple locations allows visitors to explore multiple parts of Yellowstone NP early in the day and late in the evening while minimizing driving in the dark.

There are many amazing views, and great potential for wildlife viewing and photography.  I have photographed grizzly bears, black bears, bison, moose, elk, deer, wolves, coyotes, foxes, bald eagles, ravens and crows, great blue herons, sandhill cranes, and more in Yellowstone NP.

I encourage potential visitors to go to Yellowstone NP’s Resources and Issues webpage and Download the YNP “Whole Book” (BIG PDF).  Please keep in mind that Yellowstone NP updates the resources, so the links might be changed.

If you are traveling to Yellowstone NP, I highly recommend spending some time in Grand Teton NP too.