ENThe second half of the eighteenth century was a period of dynamic change in many fields of governance in the Polish-Lithuanian Commonwealth. One of the aims of the reformers was to strengthen the state’s economy and to increase the revenue of the Treasury. In this context, reform of the customs (1764) system was of particular importance as it was meant to ensure efficient collection of customs duties. This article aims to answer the question of how the customs and border control infrastructure was created and developed, by focusing on the borderland between the Grand Duchy of Lithuania and Prussia over a period of several decades (1760s-1790s). Comprehensive and detailed reports (1769, 1788, 1793) on the border control infrastructure reflect the condition of the customs system, as well as the inspectors’ recommendations for how it could be improved. Sources such as these are not widely used in historiography, and until now there have been no attempts to compare different descriptions of the condition of the customs system. Analysing these sources allowed us to map, highlight and assess the changes to the border control infrastructure. In this article, GIS (Geographic Information System) was used as one of the analytical tools to demonstrate the interaction between border control infrastructure entities and the space of the Lithuanian-Prussian borderland. Results show that the that the development of the border control infrastructure was intensive, not extensive. It is evident that officials, even though they were well aware of illegal activities, rationally evaluated the cost-benefit ratio to the state’s resources and the potential for possible losses. The selected research approach can be applied to study other borderlands and reveals just how significant the spatial localisation of written source data can be in borderland research. Keywords: Grand Duchy of Lithuania,Kingdom of Prussia, customs, borderland, border control, smuggling.