Ljungby is a village and parish in Falkenberg Municipality, Halland County, Sweden. The name is most likely derived from the conjunction of ljung (Calluna) and by (village). It is confirmed in written sources from at least 1267. Two conurbations exist within the parish borders; Ljungby/Lilla Ljungby and Bergagård. A minor part of Ätrafors is also within the parish boundary.
The parish has an area of 54.37 km², of which 53.47 km² are land. It is mainly situated on the Hallandian plain. Arable land covered, as of 1971, about 62 percent of the parish, while 26 percent was wooded. The river Ätran delimits it in the northeast, while a tributary river, Vinån, flows through the central part of the parish. The only lake of any size is Ljungsjön, situated in the central part of the parish.
The highest shore-line passes through the parish, resulting in varied ground conditions. An ice lake delta once covered the eastern parts of the parish, leading to deposits of gravel and sand, which are being exploited. Moraine eskers are found in the northern and eastern parts. A 120 centimeter long lower jawbone from an av baleen whale has been found in Tångaberg.
The highest peak is Horsakullen, 137 meters above sea-level. Other hills are Hellepjucken (130 m), Vasabjär and Hanapjutten.
Two types of Heath plants are closely associated with Ljungby: Calluna and Broom. Calluna was previously widespread in the area, but its appearance has diminished due to modern farming. It has given its name not only to the parish, but also to several lakes, hills and farms.
Ljungby was, as of 1971, the only place in Halland, and perhaps Sweden, where Genista germanica could be found. It was also the only place in Halland north of the river Ätran wheren Silkyleaf woadwaxen could be found.