PhD study focuses on first language attrition in the Finnish language spoken by first generation immigrants who have lived in Northern California, US, for more than 20 years. While providing information about the Finnish language, it also creates novel information about the process of attrition in a morphologically complex language, especially at morphological level. As such, findings from this study will add to both, Finnish and international research, as well as to the wider field of bilingualism. In this study participants’ performances at lexical and structural levels in Finnish (L1) are studied in comparison to a control group of native Finnish speakers living in Finland. In order to gain a more holistic view of the participants’ bilingual language processing skills and the influence they may have on the language attrition process language tasks in English (L2) are also included. Within this study the modern Finnish language variant spoken in Northern California, US, is documented, preserved and analyzed for the first time. In order to preserve this variant of Finnish collected data will be stored and shared for further research purposes via Finnish Language Bank (Kielipankki, FIN-CLARIN ja CSC – Tieteen tietotekniikan keskus 2015-2016).