Sauté the celery, carrots, and onions in butter (2 tablespoons) in a large pot or Dutch oven over medium-high heat until softened (about 5 minutes).
Add the chicken stock (6 cups) and bring to a boil.
Add the wild rice along with a pinch of salt and pepper. Stir.
Cover and simmer for about 45 minutes, or until rice is cooked. Once the rice is cooked, stir in the cooked shredded chicken (2 cups) and continue simmering for 5 minutes until heated. Taste and adjust seasoning as needed. Serve.
Slow cooker instructions: Add all ingredients except for chicken into a slow cooker. Cook on low for 8 hours or high for 4 hours. Stir in the chicken at the end and heat for 5 minutes.
Freezer directions: Freeze in an airtight container for up to 6 months. When ready to eat, run warm water over the outside of the container to dislodge the soup, and heat frozen soup on the stovetop in a pot over medium heat until heated through.
A note on wild rice: I used 100% wild rice, but often you will see wild rice blends in the store, which are usually a combination of wild rice with brown rice or other rice. You can use any kind you like, but keep in mind the cooking time may vary. In addition, wild rice can take a long time to cook, depending on its age, etc. So if you are unsure, I recommend planning for more cooking time (it can take over an hour sometimes) for the rice to fully cook.
To save time, you can soak the wild rice overnight in salted water, drain and rinse, and add it as instructed in the recipe. If you do this, I recommend decreasing the chicken stock by 2 cups. Or, you can use pre-cooked wild rice- just add it in along with the chicken to heat up, and reduce the chicken stock by 3 cups.