Hi Stephanie:
By parish is the area around the present city of Säffle. It has existed as a parish since the 12th century. By parish had some big farms/manors like Krokstad, Säffle, Sund, Bäck, Norra and Södra Skane and Sjögerås, as well as several hamlets.
Säffle has always been an important location, because of the bridge over Byälven river. The rapids at the bridge had always been a problem for sailing up the river, and a canal was opened here in 1837.
The canal, and the railroad from Göteborg to Gävle passing through Säffle (opened in 1879) promoted the growth of Säffle. Several industries, including the Billerud papermill started and Säffle was groving rapidly. Säffle became a köping (town) in 1882 and was made a parish in its own right in 1911.
Parts of By parish was incorporated into Säffle. In 1943 all of the old By parish was incorporated.
Säffle became a city in 1951 and is celebrating the 50th anniversary this year.
The old parish church at By was dedicated in 1779 and is still standing. There is also a modern church in Säffle from 1965 (lutheran) and several so called free churches.
The present-day population of Säffle and By is around 11,000.
I live in Kila parish, close to Säffle.