French Algeria tended to attract immigrants from the Mediterranean basin, from various countries. Traditionally, far fewer Frenchmen emigrated from their homeland than other European countries, and by the 1850s France was experiencing net immigration. The few French who emigrated tended to be middle-class merchants to Argentina, California, Uruguay etc. Also, by 1954 79% of the 984,048 non-Muslims in Algeria were born in Algeria.
Here is a breakdown of the Europeans in Algeria by ancestry:
40% Spanish (Alicante, Murcia, Valencia and Menorca)
25% mainland France (mostly Languedoc and Provence and to a lesser extent Paris)
20% Italian (mostly Naples and Sicliy), Corsican and Maltese
12% Naturalised Jews (Granted in 1870 by the Crémieux Decree)
3% German (German, Swiss, Alsatian)
France turned to foreigners to settle not only Algeria, but Tunisia and Morocco as well. France was much more open to allowing foreigners in their colonies that most of the other colonial powers, offering them land grants for instance. In addition, the Third Republic established inclusive model of citizenship that allowed these foreigners to become French citizens. Also, the Jews of Algeria were naturalized and given the status of citizens, increasing the numbers of "Europeans" in the colony. These actions together allowed a heterogeneous mix of ethnicities to embrace their French identity, especially because they enjoyed privileges vis-a-vis the Muslim majority.
The largest single group of settlers were Spaniards, overwhelmingly from southern Spain (Provinces of Alicante, Almeria and Murcia), many came early on working as seasonal farm labourers in Western Algeria, especially Oran, which was just a ferry ride away. By the early 1900s around 30,000 arrived each year, with the majority returning to Spain. However, some remained permanently, another 30,000 Spaniards arrived as exiles during the Spanish Civil War. When independence came, some 40,000 Pieds Noirs settled in Franco's Spain.
From France, settlers came mostly from the Mediterranean basin. With the largest group coming from Corsica, nearly 100,000 Pieds Noirs were of Corsican origin by 1954, and Pieds Noirs resettled in large numbers on that island. The second largest contingent of settlers from France were from Provence and Languedoc. In addition, Algeria was used as a penal colony early on and prisoners from Paris were often exiled to Algeria during the reign of Louis Philippe. The Alsatians were fewer than 12,000 in total arriving, and they settled after 1871. There were also German-speaking Swiss and a small number of Germans that settled in small numbers earlier on.
Ethnic Italians and Maltese settled overwhelmingly in the Eastern portion of Algeria. Just as in Tunisia where over 2/3rds of the Europeans were Italians, they were mostly from Sicily. The region of Bône (Annaba) in Eastern Algeria had a non-Muslim population that was overwhelmingly Italian.