Date input format problem I need to import a large dataset (over 300,000 records) into a Drupal 8 site. I have figured out how to do this with feeds on a small test dataset. 

The dates in the records are in the format June 8, 2018. I do not see a way to use a Drupal 8 Date field to input dates in this format. 

I need to be able to create a view that displays records based on a date range. 

What is the best way to get the data into Drupal in a format that a view can use? Would it be to maybe use computed field to transform the data while it is being imported? Or would it be better to maybe execute a SQL query after the data is imported?
Rather than using Feeds, I suggest using the core Migrate module.  There is also a core plugin for converting dates during migration, FormatDate.  This will allow you do specific the input format and the output format.  I believe, this process configuration would work in your case:

process:
  field_date:
    plugin: format_date
    from_format: 'F j, Y'
    to_format: 'Y-m-d'
    source: event_date


If Feeds is your preferred method, then you can try the Feeds Tamper module.  Based on the plugin list for Drupal 8, I think you would need to do a "String to Unix timestamp" tamper on the field, followed by a "Unix timestamp to Date" tamper, using 'Y-m-d' as the format string. However, I haven't used Feeds and Feeds Tamper in a long time, and would typically write custom tampers for something like this.