By those days Dillon took charge of his family's estate in Merlo, rebuilt the town and was appointed Juez de Paz of the newly created Partido of Merlo. After his public life in Merlo, President Avellaneda appointed Dillon as Chief Commissioner of Immigration in 1875. During his administration Argentina experienced the first massive European immigration to the country and Dillon received the first Welsh immigrants, Volga Germans and Italians from Friuli. After that, Dillon and his family moves to La Plata when he was elected senator and served during three terms in the Buenos Aires legislature, in which he chaired the budget commission. 1864: Merlo obtains its autonomy In 1857 the Argentine railway company Camino de Hierro de Buenos Aires al Oeste opens the first steam locomotive public railway in Argentina and few years later the company was planning to extend the line westward to Moreno. The construction of the railway made land speculation a highly profitable activity. In order to reach Merlo the line had to pass through the land owned by the Pearson Family and Dillon saw the opportunity to make huge profits by selling out parts of the family's estate. Dillon established in Merlo and in 1859 he commissioned the famous architect and engineer Pedro Benoit to design the layout of the town, organizing it on a rectangular grid of streets and blocks. The town was enlarged and endowed with a municipal palace, avenue, train station, school and church. The rail station was opened on August 11, 1859. Dillon and others businessmen and prominent neighbors such as Manuel Rodríguez, Enrique Smith and Fernando Pearson (Juan Dillon's step brother), petitioned to the Governor the erection of a new partido from the old Partido of Morón. On October 11, 1864 the legislature of Buenos Aires sanctions the law 422 creating the Partido of Merlo. Until 1878 the new district included the today's Partido of Marcos Paz and comprehended 400 km² approx. The election of the authorities took place in the same year and only sixty-four citizens voted; the first municipal government was integrated by Juan Dillon as Juez de Paz and Antonio Suárez, Francisco Sullivan, Fernando Pearson and Tomás Gahan as Municipales or Councilors. Thousands of neighbors fled Buenos Aires to the countryside when a cholera epidemic first, and a yellow fever outbreak later, afflicted the city in 1867 and 1871 respectively. These events brought many Spaniard, Basque, Italian