Gjerstad is a municipality in Agder county, Norway. It is located in the traditional region of Sørlandet, in the southeastern part of the county, along the border with Telemark county. The administrative centre of the municipality is the village of Gjerstad. Other villages in the municipality include Ausland, Eikeland, Fiane, Gryting, Østerholt, Rød, Sundebru, and Vestøl. The municipality is the 256th largest by area out of the 356 municipalities in Norway. Gjerstad is the 258th most populous municipality in Norway with a population of 2,427. The municipality's population density is and its population has decreased by 2.1% over the previous 10-year period. The parish of Gjerstad was established as a municipality on 1 January 1838 (see formannskapsdistrikt law). The borders have not changed since that time. The municipality (originally the parish) is named after the old Gjerstad farm (Geirreksstaðir) since the first Gjerstad Church was built there. The meaning of the first element is uncertain. One possibility is that it is the genitive case of the male name Geirrekr. Another possibility is that it comes from the word geirr which means "spear". The last element of the name is the plural form of staðr which means "place", "abode", or "town". Historically, the name of the parish was spelled Gerikstadum (c. 1400), Gierestat (c. 1567), Gierrestad, and Gjerrestad. The coat of arms was granted on 18 April 1986. The official blazon is "Gules, three knives argent in fess palewise points to the base" (På raud grunn tre opprette sølv knivar). This means the arms have a red field (background) and the charge is three knives pointing downwards. The knives have a tincture of argent which means it is commonly colored white, but if it is made out of metal, then silver is used. The knife was chosen as a symbol for the smithies and knife makers in the municipality. Knife making has long been a local tradition for which Gjerstad is well known. The arms were designed by Odd Kjell Mostad. The municipal flag has the same design as the coat of arms.