ApexClass

public class AggregateStateInfo
{
    @InvocableMethod
    //Method that accepts the Account ID
    {
        // Find all related Location_Information__c records and store the State__c value in a collection variable
        // Make sure the values are not duplicates
        // Update a custom field on Account (Aggregated_State_Info__c [Text type]) with the de-duplicated States separated by a comma
    }
}