The name of the commune appeared already in the papal tithe register of 1332. Every troop, the Turk, Tartar, Cossack or Russian ones which entered Trei Scaune, had to pass through Lemnia. Kemeny Janos ruler rested here in 1653. In 1694 it was mentioned as a village in the foreground of the passage of Bretcu. General Bern passed here in 1849 when he was coming from an unsuccessful Moldavian visit (his name is beard by the local school), he was accompanied by the poet Petofi Sandor as well.
Already in the Roman period this road was the main trading and military road, it was the street of bartering between Transylvania and Moldova. The real development of the commune started in the second part of the 19th century.
Its agricultural territory is not extended, its soil is quite poor. The main economic branch was livestock-breeding along with making of hay and after grass. Besides, timber industry and lumbering are also present. Its agricultural character is kept even today.
Conversion of timber can be said to be a new industrial branch, several wood-working sites are functioning. There is an abattoir and a butchery as well. According to the census of 2002 the population of Lemnia counts 2044 inhabitants out of which 1,95% are Romanians, 98,43% Hungarians and 0,42% are Hungarian-speaking Roms. The most important architectural monument in Lemnia is the Roman Catholic monument group of Baroque style surrounded with a protecting wall. The originally Gothic church was rebuilt in the Baroque period. It is one of the most beautiful Baroque monuments of the whole region. The gables are foiled and there are volutes and niches for statues on them.
On its painted ceiling we can wonder the frescos depicting St. George, St. Michael and the Holy Trinity. The picture of its late Baroque high altar was painted in 1899 by baron Szentkereszti Stefania, it depicts the patron saint of the church, namely St. Michael archangel. It has a precious old relic, the chalice-shaped medieval baptistery. Its bell-tower is covered by a Baroque bulbous dome. One of its bells dates back to 1697. Other architectural interests are the St. John-chapel and the old Sebestyen's water-mill and fulling-mill in Lemnia de Sus (they were built in the 19th century, they are not functioning today).
An old folk custom has been revived in the last few years, namely the owl's burial; in fact it is the holiday of burying the winter. In the past the living owl symbolized the winter in the eyes of the people, now they forget the pagan custom and they are burying a stuffed owl. Here the old Easter custom, namely the ,,beat the bounds" is living as well. On Easter day the young men are putting green branches to the gates of the girls, the children are going from house to house on Childermas-day (28th of December) and the rhymed greetings on Istvan's and Janos's days are also living. In the place named Almasret we can find many thatched cottages. There is a piece of rock on which - according to the oral tradition - Jesus' footprint can be seen. Natural curiosities are the sulphurous springs rushing up from the palaeocene sandstone of the Farkas brook and of the River Haul Negru's valley. From Lemnia we can approach the Apa Rosie valley situated beyond the main crest line of the Carpathians. Here we can find the botanical reservation called ,,The Bog of Apa rosie" in 1040 meters height.
It is the home of rare plants such as the rotundifolious sundew, the Siberian ash flower and a kind of bog-moss of Boreal origin (Sphagnum wulfianum). A marked pathway leads from the commune to the Nagy San-dor-peak (1646 m) and to the Nemira Mare (1653 m) placed behind the former one. From its top - in a bright day - we can sight ,,Moldova's pearl", Slanic Moldova.