You might get confused when you try to hide the site name in Drupal 8 if you are looking for this setting in the theme settings page like I did. The answer is that these settings to hide logo, site name and slogan are now contained within a block. In order to hide your site name follow the steps below.
Step 1. Log into your Drupal 8 admin area
Step 2. Click Structure -> Block Layout
Step 3. Find a block named "Site Branding", click configure
Step 4. Un-check "Site Name" under "Toggle Branding Elements"