Cook bacon pieces in a large skillet over medium-low heat until just crisp. Remove from skillet and set aside for later use. Leave bacon drippings in the skillet. Add chicken thighs to the skillet and brown on each side. Remove from skillet and set aside on a plate for later use. Add onions, garlic, mushrooms, celery, and carrots to the skillet and cook for about 5 minutes to lightly brown. Add a drizzle of olive oil if needed. Remove from skillet and add to the insert of the slow cooker.
Add chicken thighs to the slow cooker insert on top of the vegetables. Sprinkle with the bacon pieces.
Pour in the chicken stock and add the thyme.
Cook on low for 6-8 hours or on high for 3 hours.
Notes
Cooking time includes browning of recipe contents prior to cooking in slow cooker as well as slow cooking on low for 6 hours.