Georgia Declares Independence. May 26, 1918.

Not from Russia, however, but from the Transcaucasian Federation, which also included Azerbaijan and Armenia. They'd follow by declaring independence a couple of days later.

Flag of Georgia, 1918-1921

The declaration came under the stress of an invasion by the Ottoman Empire which first recognized the Transcaucasian Federation and then invaded it.  The federation was always weak and it cracked under the in ability to defend itself, dissolving into national units where its loyalties actually lay.  Georgia's Menshevik Social Democratic Party would lead the withdraw and won the subsequent parliamentary election, making Georgia an independent radically socialist state.

It's independence would be short lived, although it managed to get into a war with Armenia during it.  In 1921 the Red Army entered the country and ended its independence until 1991.

Georgian soldiers in Iraq in 2006 celebrating their May 26 independence date under their current flag.