Namdalseid is a former municipality in Trøndelag county, Norway. The municipality existed from 1838 until its dissolution in 2020 when it joined Namsos Municipality. It was part of the Namdalen region. The administrative centre of the municipality was the village of Namdalseid. Other villages and farm areas in the municipality included Sjøåsen, Statland, Tøttdalen, and Sverkmoen. At the time of its dissolution in 2020, the municipality was the 144th largest by area out of the 422 municipalities in Norway. Namdalseid was the 348th most populous municipality in Norway with a population of 1,585. The municipality's population density was and its population had decreased by 7.7% over the previous decade. The parish of Namdalseid was established as a municipality on 1 January 1838 (see formannskapsdistrikt), but it was merged into the neighboring municipality of Beitstad on 1 January 1846. On 1 January 1904, the Namdalseid district (population: 1,368) was separated from Beitstad to form a municipality of its own (once again). During the 1960s, there were many municipal mergers across Norway due to the work of the Schei Committee. On 1 January 1964, the parts of the neighboring municipality of Otterøy that were located south of the Namsenfjorden (population: 571) were transferred to Namdalseid municipality. On 1 January 2018, the municipality switched from the old Nord-Trøndelag county to the new Trøndelag county. On 1 January 2020, the neighboring municipalities of Fosnes, Namsos, and Namdalseid merged to form a new, larger Namsos Municipality. This occurred because on 16 June 2016, the three municipalities voted to merge as part of a large municipal reform across Norway. The municipality (originally the parish) is named Namdalseid. This name originally comes from the old Elda farm (Eldueið or commonly shortened to Eið) since the first Eid Stave Church was built there. The first element is eldu which is the name of the local river. The last element is eið which means "path/road between two waters" (here the Beitstadfjorden and Namsenfjorden)".