Pets are welcome at Mount Rainier, but they and their owners must practice the following:

At all times, pets must be on a leash not more than 6 feet in length or in a cage.

At all times, pets must be with and under the control of their owners.

Owners must pick up and dispose of all fecal matter.

Where are pets permitted at Mount Rainier?
Pets are permitted in parking lots, campgrounds, and on paved roads. While in these areas, pets must, at all times, be leashed or crated and with their owners.

The Pacific Crest Trail is the one exception to this rule. Dogs on a leash no longer then 6 feet are permitted on the Pacific Crest Trail.
 
At Mount Rainier, pets are NOT allowed in the following areas  (service animals excepted):

On trails
Inside buildings
In the wilderness
In amphitheaters
On snow

For the safety of your pet and the benefit of park wildlife and other visitors, never leave your pet unattended in a vehicle or in the campground. 

Mount Rainier National Park does not have kennel facilities.