I've seen so many birthdays for Hetalia characters that coincide with national holidays and occurances that I wanted to try this myself. I had to fill the void with other nations. And for other characters, I'll explain who they are at the end of this journal. This entry will be updated with more nations to come. Feel free to add your comments below and I'll try to answer as many questions as possible.
HETALIA BIRTHDAYSJanuary 5PICARDY
January 11CHECHNYA
January 16ANCIENT ROME
January 18GERMANY
January 24ROMANIA
January 26AUSTRALIA
February 2HOLY ROMAN EMPIRE
February 3GREECE
February 11JAPAN
February 12SPAIN
February 16LITHUANIA
February 24ESTONIA
February 28EGYPT
March 15HUNGARY
March 17ITALY (ROMANO, VENEZIANO/CHIBITALIA)
April 10PRUSSIA
April 12CONFEDERACY
April 22HWF MASTER
April 23ENGLAND
April 24IRELAND
May 3NORTHERN IRELAND
May 14ISRAEL
May 17NORWAY
May 20CUBA
June 5DENMARK, PICTONIANS
June 6SWEDEN
June 12PHILIPPINES
June 17ICELAND
June 29SEYCHELLES
June 30UKRAINE
July 1CANADA
July 4AMERICA
July 11WALES
July 12LIECHTENSTEIN
July 14FRANCE
July 21BELGIUM
July 22POLAND
July 26NETHERLANDS
August 1SWITZERLAND
August 15SOUTH KOREA
August 25BELARUS
September 2VIETNAM, SEALAND
September 9NORTH KOREA
September 11SCOTLAND
September 16MEXICO
October 1CYPRUS
October 3GERMANIA
October 10CHINA
October 24UNITED NATIONS
October 26AUSTRIA
October 29TURKEY
November 15NORTHERN CYPRUS
November 18LATVIA
December 6FINLAND
December 25TAIWAN
December 29MONGOLIA
December 30RUSSIA
HWF Master is a character I created for my project "Hetalia Wrestling Federation". He's a cross between Andre the Giant, Yokozuna and Bane of the Batman series. Basically, he's the embodiment of the world's wrath, hence why I put April 22 for his birthday, coinciding with Earth Day.

There is officially no
Chechnya in Hetalia, but I decided to make one from the real anime. He's the one arrested for computer hacking in HBW Episode 8: "The Gentle Fight Between Russia and I". I'll try to think of a name that suits him best later on.

I couldn't find the exact date that
Germania, Germany and Prussia's grandfather, was born, so I decided to use the date that East and West Germany reunited.
The Pictonians are aliens and don't have Earth days, so why did I put them having June 5 alongside Denmark? Because "Hetalia the Movie: Paint it White!" was released on that date. You could also call it "Pictonian Day" if you wish.

In the anime, there's an old man Japan was thinking of. He is the embodiment of the
United Nations itself. October 24, 1945 is when the U.N. was established. Coincidentally, October 24 is also Hetalia Day. Squee! ^∀^

Many people have their own version of the
Confederacy, or the Confederate States of America. April 12, 1861 was the beginning of the American Civil War.