Update the Salesforce Last Modified Date When There is a New Case Comment

To update the Last Modified Date on a Case when a new Case Comment is added, create a custom Date/Time field on the Case object and configure automation on the Case Comment object to update that field whenever a comment is created or modified. Updating the custom field causes the Case record to be updated, which also updates the Last Modified Date.

Method 1: Using a Workflow Rule

1. Create a Date/Time field on the Case object. This field does not need to be added to the page layout.
2. Create a Workflow Rule on the Case Comment object that triggers every time a record is created or edited.
3. As the Workflow Criteria, use a formula that always evaluates to True.
4. Add a Field Update action that updates the custom Date/Time field you created on the Case.
5. Set the field value using the formula NOW().
6. Save the Workflow Rule.

Each time a Case Comment is added or modified, the custom Date/Time field is updated with the current date and time, which in turn updates the Last Modified Date on the Case.

Method 2: Using Process Builder

1. Create a Date/Time field on the Case object. This field does not need to be added to the page layout.
2. Create a Process Builder on the Case Comment object that triggers every time a record is created or edited.
3. Set Define Criteria for this Action Group to No criteria — just execute the actions!
4. Under Immediate Actions, choose Select a record related to the CaseComment.
5. Select Parent ID.
6. Select the custom Date/Time field you created on the Case.
7. For the Process Builder method, set the value of the custom Date/Time field using the formula NOW().
8. Save and activate the process.