| Official Name: | Söderby-Karl |
| Pushpin Map: | Sweden Stockholm#Sweden |
| Subdivision Type: | Country |
| Subdivision Name: | Sweden |
| Subdivision Type3: | Municipality |
| Subdivision Name3: | Norrtälje Municipality |
| Subdivision Type2: | County |
| Subdivision Name2: | Stockholm County |
| Subdivision Type1: | Province |
| Subdivision Name1: | Uppland |
| Area Footnotes: | [1] |
| Area Total Km2: | 0.67 |
| Population As Of: | 31 December 2010 |
| Population Total: | 231 |
| Population Density Km2: | 345 |
| Timezone: | CET |
| Utc Offset: | +1 |
| Timezone Dst: | CEST |
| Utc Offset Dst: | +2 |
| Coordinates: | 59.8864°N 18.6994°W |
Söderby-Karl is a locality situated in Norrtälje Municipality, Stockholm County, Sweden with 231 inhabitants in 2010.
Söderby-Karl Church, dating from the Middle Ages, lies in Söderby-Karl.