He retired in 1821 and died in the same year. Sommerfelt was also elected to the first Parliament of Norway in 1814, and served through the one-year term. As an Enlightenment person, Sommerfeldt was interested in practical agriculture, economy and topography. He was the praeses of "Det Romsdalske practiske Landhusholdningsselskab" in the early 1800s, and while serving in Christians Amt he advocated the city status for Lillehammer, which was granted in 1827. In Finmarkens Amt he planned the city status for Tromsøe (granted 1794) and achieved city status for Vardø and Hammerfest in 1789. He followed a free trade principle and also supported Jens Holmboe's settling project in Målselvdalen. Like his brother, he was also a topographical writer. The journal "Topographisk Journal for Norge" printed his main topographical work, "Kort Beskrivelse over Finmarken", in 1799. Sommerfelt was decorated as a Knight of the Order of the Dannebrog (1813), the Order of Vasa (1815) and the Order of the Polar Star (1818). He died in April 1821 in Biri and was buried in Vardal.