In this dataset, we provide the raw data of a corpus-based investigation of French loan suffixes in Dutch sailing letters, as well as a set of metadata used to investigate the impact of sociolinguistic variables related to the scribe of each letter. The data accompanies the research reported on in Rutten & Vosters (2023), which delved into the use of 31 French loan suffixes (e.g. the verbal suffix -eren, nominal suffixes such as -age and -teit, and adjectival suffixes such as -aal) in the Letters as Loot Corpus, which is a socially stratified corpus of private and business letters from the seventeenth and eighteenth centuries, written by men and women from various regions in the northern Low Countries. Rutten, G., & Vosters, R. (2023). Testing Frenchification. A sociolinguistic analysis of French loan morphology in seventeenth- and eighteenth-century Dutch. Roczniki Humanistyczne, 71(6), 225–248.