It is at the mouth of the Lega river which flows into the Great Olecko Lake (Jezioro Oleckie Wielkie) on its southwestern shore.

[2] The town's coat of arms still reflects the Brandenburg red eagle and the Hohenzollern black and white which go back to Duke Albert.

[2] Already in 1560, the new residents appointed a town council and municipal court and selected fellow Pole Stanisław Milewski as the first mayor.

[6] In June 1807, Polish soldiers of General Józef Zajączek took Olecko, then left the town to be replaced by the 2nd Infantry Regiment of Jan Henryk Dąbrowski.

[10] The synod's protest was signed by all the pastors in the county, and its arguments were later used by the well-known defenders of the Polish language in Masuria, Gustaw Gizewiusz and Krzysztof Celestyn Mrongovius.

[12] In 1920, after Poland regained independent existence following World War I, a plebiscite was to be held in the area by the League of Nations, according to the Treaty of Versailles, to determine the future of the region and the town.

During World War II, many Poles, but also some Belarusians, Ukrainians and Russians, were enslaved by the Germans as forced labour in the town's vicinity.

The abandoned town was captured by the Red Army on January 23, 1945, and afterwards it became again part of Poland under territorial changes promulgated at the Potsdam Conference in July–August 1945.

The town was repopulated by Polish settlers, both from nearby Suwałki and Podlachia regions, and from former eastern Poland annexed by the Soviet Union.

The Olecko train station in the western part of town is a regional railway junction: there were main lines to Gołdap, Ełk and Suwałki.

[18] The town's leading sport club is Czarni Olecko [pl] with football, handball, table tennis and chess sections.