The Vlach peoples in northern Bulgaria are often referred to as "Romanians" as they speak the Romanian language. However, when considering there identity based on nationality the term "Romanian" is misleading as many of these peoples, particularly in the Timok valley and Vidin regions, are most probably indigenous to these regions and do not have a connection to the nation of Romania founded in the mid 19th century.
The greatest density of Vlachs are the areas north and west of Vidin and along the Timok valley (now partly in Serbia). The census data shows a rapid decline in those declaring themselves as Vlach or Romanian between the 1920s and the 1930s, may be the data collected is based on "nationality" which would be Bulgarian, rather than ancestral identity.
In the early 19th century the Vlach proportion in Vidin region was probably around 20%, with most of the northern villages being Vlach. The numbers acknowledging a Vlach identity may be very low now, but the traditional costume, dance and music of this region is still Vlach and very closely associated with that of Oltenian Romania.
Vratsa and Pleven regions have a small number of Vlach villages mainly along the Danube between Lom and Nikopol. There may also small pockets of Vlachs and Romanian speakers in other villages, our Bulgarian friend from Pleven tell us that there are also in Pavlikeni.
Popescu-Spineni, M., Noe, C. (1939), I Romeni in Bulgaria, Editura Ramura, Craiova