The main aim of this study is to shed light on a phenomenon of migrants´ illegal crossing of the Czech state border, to enrich official statistics by own empirical research. One specific data set providing information about who was going to cross, or, has already crossed, the Czech state border, and how, is used and analysed. The article offers the results of a questionnaire survey carried out with 99 illegal migrants who tried or successfully completed crossing of the Czech (and sometimes other) state border(s), were apprehended by the Czech Police and held in detention centres. The results tell us that those who arrived to Czechia illegally have some specific characteristics and behavioural models vis-à-vis those who came to the country legally. Authors believe that despite joining the "Schengen Agreement" in December 2007 and, thus, abolishing the “classical outer state borders” of Czechia, such analytical experience is worth “testing” now in other European Union (EU) Central/Eastern European countries that border on the “third-country world”.