US Calendar

Here is a second option if the Gif below doesn't work

How to add the US Calendar to your iPhone Calendar App

1. Open the Calendar app
2. Select "Calendar" from the bottom section of the app
3. Scroll down to the "Other" section
4. Select "US Holidays"

Try checking your Region / Language settings

1. Go to Settings
2. Select "General"
3. Tap "Language & Region"

Double check that the Region section is set to the United States.

Have you tried this? Watch the GIF below.