Lagmansö, Manor house in Vadsbro parish, Flens municipality, Sweden

Lagmansö is a two-storey manor house completed in the 1770s on a peninsula in Lake Långhalsen, in Vadsbro parish, Flens municipality, Södermanland. Its present appearance follows drawings by Gustaf Sjöberg, and it serves as the main estate of a Falkenberg family fideicommissum.

Lagmansö is first mentioned in 1336 as "Lagmanzhøø" and was a seat farm for councillor Sigge Magnusson of the Vinstorpa family until 1358. Through inheritance it passed to Ulf Bengtsson (Sparre) in 1392, Gustav Algotsson (Sture) in 1433 and Elin Gustavsdotter Sture in 1475. In 1544 Göran Åkesson (Tott) gave it as morning gift to his wife Kristina Larsdotter. In 1774 governor Baron Gabriel Falkenberg af Trystorp made the estate a fideicommissum, and the two-storey main building from the 1770s stands on a peninsula in Lake Långhalsen.

The name Lagmansö appears in documents as early as 1336, when it was written "Lagmanzhøø". The estate has belonged to the baronial Falkenberg af Trystorp family since Kristina Maria Kruse married Henrik Falkenberg, and in 1774 Gabriel Falkenberg made it an entailed estate (fideikommiss). The two-storey main building, on a peninsula in Lake Långhalsen, took its present form after drawings by Gustaf Sjöberg.

Lagmansö is reachable by car from Stockholm, with the drive taking around two hours across countryside roads in Södermanland. Being located in a rural area means visitors should plan transportation in advance.

In 1544, Göran Åkesson (Tott) gave Lagmansö as a morning gift to his wife Kristina Larsdotter (Sparre av Rossvik); she later lived here as a widow and then with her second husband Måns Pedersson (Lilliehöök), who died in 1562. That year the estate's dependent farms were listed, from Österö in Vadsbro to Händö and Röl in Dunkers parish.