This research is a first attempt to investigate the Bolivian immigration based on population census and marriage certificates. The Bolivian immigration in the province of Tarapacá will be based on the description and analysis of demographic variables, such as number, gender and age distribution. According to the statistics, it is possible to develop a demographic profile of Bolivian immigrants who arrived during the nitrate cycle expansion. The results will allow us to affirm that they got increase numerically during the turn of the century, characterized by a relative balance of men and women, mainly active young single people, from Cochabamba. Furthermore, most of the men were inserted into primary activities; meanwhile women were in the tertiary sector. Finally, this article will try to elucidate who formed the society of Tarapacá in the second half of the nineteenth century, knowing in detail what the reason of marriage for the Bolivian immigrants was. Specifically, in comparison with the Chilean population which was the owner of these lands after the triumph of the Pacific War and also because it was the majority of population with respect to the sum of Peruvian, Argentinean, European and Asiatic inhabitants.La investigación que presentamos es un primer intento de dimensionar la inmigración boliviana sobre la base de censos de población y actas matrimoniales. De acuerdo con las informaciones estadísticas elaboramos un perfil demográfico de inmigrantes bolivianos que arribaron durante el ciclo de expansión salitrero, cuyos resultados nos permiten afirmar que ellos aumentaron numéricamente durante el cambio de siglo, caracterizado por un relativo equilibrio de hombres y mujeres, jóvenes solteros en edades laborales activas, provenientes principalmente de Cochabamba. Además, la mayoría de los varones se insertó en actividades primarias, en cambio, la mujer en el sector terciario. En último término, para dilucidar quienes conformaron la sociedad de Tarapacá en la segunda mitad del siglo XIX, quisimos conocer en detalle en qué se tradujo la decisión matrimonial de los inmigrantes bolivianos. Específicamente, tomando como sociedad receptora a la chilena por tener la mayor presencia numérica en comparación a la suma de peruanos, argentinos, europeos, y asiáticos, y por ser la dueña de estas tierras después del triunfo de la Guerra del Pacífico.