Claim: Lithuania's largest city has a population of 542,664.

Lithuania -LRB- UK and US : -LSB- lɪθuː ` eɪniə -RSB- , Lietuva -LSB- lʲɪɛtʊˈvɐ -RSB- -RRB- , officially the Republic of Lithuania -LRB- -LSB- Lietuvos Respublika , links = no -RSB- -RRB- , is a country in Northern Europe . One of the three Baltic states , it is situated along the southeastern shore of the Baltic Sea , to the east of Sweden and Denmark . It is bordered by Latvia to the north , Belarus to the east and south , Poland to the south , and Kaliningrad Oblast -LRB- a Russian exclave -RRB- to the southwest . Lithuania has an estimated population of 2.8 million people , and its capital and largest city is Vilnius . Lithuanians are a Baltic people . The official language , Lithuanian , along with Latvian , is one of only two living languages in the Baltic branch of the Indo-European language family .   For centuries , the southeastern shores of the Baltic Sea were inhabited by various Baltic tribes . In the 1230s , the Lithuanian lands were united by Mindaugas , the King of Lithuania , and the first unified Lithuanian state , the Kingdom of Lithuania , was created on 6 July 1253 . During the 14th century , the Grand Duchy of Lithuania was the largest country in Europe ; present-day Lithuania , Belarus , Ukraine , and parts of Poland and Russia were the territories of the Grand Duchy . With the Lublin Union of 1569 , Lithuania and Poland formed a voluntary two-state union , the Polish -- Lithuanian Commonwealth . The Commonwealth lasted more than two centuries , until neighboring countries systematically dismantled it from 1772 -- 95 , with the Russian Empire annexing most of Lithuania 's territory .   As World War I neared its end , Lithuania 's Act of Independence was signed on 16 February 1918 , declaring the founding of the modern Republic of Lithuania . In the midst of the Second World War , Lithuania was first occupied by the Soviet Union and then by Nazi Germany . As World War II neared its end and the Germans retreated , the Soviet Union reoccupied Lithuania . On 11 March 1990 , a year before the formal dissolution of the Soviet Union , Lithuania became the first Soviet republic to declare itself independent , resulting in the restoration of an independent State of Lithuania .   Lithuania is a member of the European Union , the Council of Europe , a full member of the Eurozone , Schengen Agreement and NATO . It is also a member of the Nordic Investment Bank , and part of Nordic-Baltic cooperation of Northern European countries . The United Nations Human Development Index lists Lithuania as a `` very high human development '' country . Lithuania has been among the fastest growing economies in the European Union and is ranked 21st in the world in the Ease of Doing Business Index .