Cooking chicken breast in a crock pot (also known as a slow cooker) typically takes about 4 to 6 hours on the low setting or 2 to 3 hours on the high setting. The exact cooking time can vary depending on the size and thickness of the chicken breast, the specific crock pot model, and the recipe being used.
For food safety reasons, it's important to ensure that the internal temperature of the chicken reaches a minimum of 165°F (74°C) to ensure it's fully cooked and safe to eat. To be certain of reaching this temperature, you can use a meat thermometer to check the chicken's internal temperature at the thickest part of the breast before serving.
Keep in mind that slow cookers can vary in their heating elements and settings, so it's always a good idea to refer to the specific recipe you are using or consult the manufacturer's guidelines for your crock pot model. Additionally, if you're cooking chicken breasts with bones or using bone-in chicken, it may require slightly longer cooking times compared to boneless, skinless chicken breasts.