Europe
We track 43 countries in Europe. The average current leader has been in office 2,050 days (about 5.6 years). The longest-serving is Hans-Adam II, Prince of Liechtenstein of Liechtenstein, at 13,440 days. By the Regimes of the World classification, 32 countries count as democracies and 6 as autocracies.
Regime classifications follow the Regimes of the World scheme (V-Dem), via Our World in Data.