Europe
We track 44 countries in Europe. The average current leader has been in office 2,504 days (about 6.9 years). The longest-serving is Hans-Adam II, Prince of Liechtenstein of Liechtenstein, at 13,441 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.