Shimoina (下伊那郡 Shimoina-gun) is a district located in Nagano Prefecture, Japan.
As of May, 2008, the district has an estimated Population of 65,359 and a Density of 51.4 persons/km². The total area is 1,270.43 km².
There are 3 towns and 10 villages within the district.
- 1878: The district was formed out from Ina District. The seat was located at Iida.
- July 1, 1993: The town of Kamisato merged into the expanded city of Iida.
- October 1, 2005: The villages of Kami and Minamishinano merged into the expanded city of Iida.
- January 1, 2006: The village of Namiai merged into the village of Achi.
- March 31, 2009: The village of Seinaiji merged into the village of Achi.
Coordinates: 35°25′55″N 137°44′24″E / 35.432°N 137.74°E