Prior to 19th century, the entire castle-rich Belarusian-Lithuanian frontier was inhabited by ethnic Lithuanian majority. Historically the Lithuanian nation was dominant in a far larger territory than the modern-day Republic of Lithuania. This is still visible in placenames: a lot of them in northwestern Belarus are of Lithuanian origin (the endings are Slavicised: Trakeli, Lazdūny, Kiemeliški, Gulbiny, Kiškeliški...). The letters "išk" ("ishk", "iszk") are unique to Lithuanian-origin placenames.
Lithuanians of the assimilated into Slavic communities during the Russian Imperial and Soviet onslaughts of russification. Russian Empire banned Lithuanian language in the mid-19th century and while the people of western Lithuania found it easier to illegally import Lithuanian books from Germany this was not the case in modern-day Belarus. The percentage of Lithuanian native speakers in Vilnius governorate (which included much of modern-day Belarus) decreased from 35%-40% in mid-19th century to 17%-20% in ~1914. After a short Lithuanian rule, the region was captured by Poles in 1920 and the ongoing Polish-Lithuanian conflict over Vilnius led to further discrimination of the minority. The final blow was, however, the Soviet policies. Many Lithuanian majority areas were added to Soviet Belarus instead of Soviet Lithuania, all Lithuanian schools were then closed and even public speaking in Lithuanian prosecuted. In this era many Lithuanians left for Lithuania, others adopted the Russian language.
Several territories still contain Lithuanian communities. The largest of them is around Gerviaty (Gervėčiai) village (~14 villages, 9 of them Lithuanian-majority). Some 1000 Lithuanians live there today. A Lithuanian cultural center and Lithuania-funded Lithuanian school (Rimdžiūnai village) are at heart of the community. While the older generations associate themselves with Lithuania, the kids rarely speak Lithuanian natively. The choice of whether to send them to Lithuanian or Belarusian school typically depends on the future their parents expect for them. The Lithuanian school even has some Belarusian students who are being prepared by their families for an emigration to richer Lithuania. In Mykoliškės (Michailiški) village near Gerviaty (Gervėčiai) a new Astravec Nuclear Power Plant is under construction. Its workers are brought in by Russia and some Lithuanian-owned homes were demolished to make a place for new constructions.
The most impressive building in Gervėčiai area is the gothic revival Gervėčiai church (1903). Lithuanian in style and massive size (62 m tall tower) it outflanks the 600-strong village. In fact, it is the largest Catholic church in Belarus and is still adorned by Lithuanian inscriptions and surrounded by tall elaborate Lithuanian wooden crosses (Lithuanian art of crossmaking is an immaterial UNESCO World Heritage).
Other Lithuanian majority areas that survived until the Soviet occupation (1939) now are almost destroyed. These are the villages around Varanavas, Pelesa, Apsas, Lazdūnai. Pelesa still hosts a Lithuanian-language school funded by the Lithuanian government.
Even those regions where Lithuanian language is no longer spoken at all still are distinctive from the rest of Belarus. Catholic religion dominates there instead of Russian Orthodoxy, some Lithuanian traditions also survive.
In addition to the centuries-old aforementioned communities, the 19th century Russian Imperial occupation led to the creation of new Lithuanian communities even in the eastern Belarus. With no limits on internal migration, some Lithuanian peasants left for eastern Belarus to establish Lithuanian villages such as Malkava (now Malkovka). Unfortunately, the Soviet deportations and russification totally uprooted these communities.