Orsa is a locality and the seat of Orsa Municipality, Dalarna County, Sweden, with 5,308 inhabitants (2010). It is located in the northern part of lake Siljan, about 15 kilometres north of the town Mora. Inlandsbanan and European route E45 run through the town and the railroad Bollnäs-Orsa connects.

Siljan, in Dalarna in central Sweden, is Sweden's seventh largest lake. The cumulative area of Siljan and the adjacent, smaller lakes Orsasjön and Insjön is 354 km2 (137 sq mi). Siljan reaches a maximum depth of 134 m (440 ft), and its surface is situated 161 m (528 ft) above sea level. This renders the lowest point of the basin at 27 metres (89 ft) above sea level. The largest town on its shore is Mora.