St Stephen's Day applies in Zürich, Bern, Luzern, Uri, Schwyz, Obwalden, Nidwalden, Glarus, Zug, Freiburg, Solothurn, Basel-Stadt, Basel-Landschaft, Schaffhausen, Appenzell Ausserrhoden, Appenzell Innerrhoden, St. Gallen, Graubünden, Aargau, Thurgau, Tessin, Wallis, Neuenburg. Outside these cantons, the date can be a normal working or school day.
Not included or not treated uniformly: Waadt, Genf, Jura.
For cross-canton planning, write the canton into the calendar entry. Otherwise childcare, meetings, travel and opening hours are easy to misread.