Many US citizens will never have a large enough estate to have to worry about the Federal Estate Tax (as of now the minimum threshold is $11.2M for individuals and $22.4M for married couples). However, each individual state also may have its own Estate and/or Inheritance Tax.
For example up until January 1, 2018, New Jersey had both an Estate and an Inheritance Tax. In 2017, if a NJ resident had an Estate valued at over $2M could have an Estate Tax added up to 16%. However, even to this day, If any person, regardless of domicile, who is not a direct descendant (children, grandchildren, parents, grandparents, spouses), received an Inheritance from a NJ domiciliary they may have to pay an Inheritance Tax.
In fact there are 6 states with Inheritance Taxes, and 13 states (plus the District of Columbia) that have Estate Taxes. Make sure you know the rules of your jurisdiction before it becomes too late and you have to pay penalties for failure to file.
And, never forget, you may have Income Taxes to claim as well.