Yes, 2.3 billion voters, which country has that many? India? No not quite - over a billion though. China? No, only half that many. USA? Nope, fewer than 300 million registered voters - just a tiddler in the democracy stakes.
Since you'll never guess, I'll tell you - it's the United Kingdom! That's because all Commonwealth and all European Union citizens can vote in the UK (subject to coming here and putting their names on the list.)
I guess that makes us the biggest democracy in the world. Unfortunately it means our government is far keener on pandering to foreigners than looking after the interests of the natives of these Islands.