Östergötland County (Östergötlands län) is a county or län in southeastern Sweden. It has land borders with the counties of Kalmar to the southeast, Jönköping to the southwest, Örebro to the northwest, and Södermanland to the northeast. It also has a sea border with Västra Götaland to the west (across lake Vättern), and borders the Baltic Sea to the east.
Östergötland County has a population of 429 852 (March 31, 2011) and the capital and biggest city is Linköping. Linköping and neighbouring twin city Norrköping together form one of Sweden's metropolitan areas; The Linköping-Norrköping Corridor is therefore sometimes referred to as The Fourth Metropolitan Region of Sweden, the other three being Stockholm, Gothenburg and Malmö.