Most countries to be Head of State of simultaneously
Who
Queen Elizabeth II
What
16 total number
Where
Not Applicable ()
When
2016

In terms of the number of independent nations for which the same person is lawfully Head of State at the same time is 16 and belongs to Her Majesty, Queen Elizabeth II (UK) – possibly the most powerful woman in the world. While the Queen's role is nominal and ceremonial (exercising no political powers), more than 139 million people in 15 Commonwealth states (plus the UK) recognize her as their monarch.

These 16 are: Antigua & Barbuda, Australia, The Bahamas, Barbados, Belize, Grenada, Jamaica, New Zealand, Papua New Guinea, St Christopher and Nevis, St. Lucia, St. Vincent and the Grenadines, Solomon Islands, Tuvalu. There are 52 states in the Commonwealth. Most were either once British colonies or were dependencies of those colonies.

The Queen’s official title is: "Elizabeth the Second, by the Grace of God of the United Kingdom of Great Britain and Northern Ireland and of Her other Realms and Territories Queen, Head of the Commonwealth, Defender of the Faith".