Kao naselje koje se nalazi na graničnoj liniji između prostora negdašnje Dubrovačke Republike i negdašnje Mletačke Dalmacije, Blato, uz tipična obilježja otočkih, ruralnih, srednjedalmatinskih naselja, prima pozitivne demografske utjecaje s juga i po mnogim je pokazateljima vrlo blisko otoku Lastovu, graničnom otoku, ali s dubrovačke strane. U razdoblju od 1870. do 1880. godine u Blatu se jasno očituju prvi simptomi demografske tranzicije: smanjen mortalitet, porast stanovništva, visoka ženidbena dob, produljen ljudski vijek. Tranzicija je na samome početku i zahvatila je samo mortalitet staračkog kontingenta, dok je mortalitet dojenčadi još uvijek izrazito visok.Analysis has confirmed that Blato followed the major demographic trends observed on the central Dalmatian islands, which, in numerous details, showed sharp dissimilarities from the Dalmatian mainland. The specificities of Blato demonstrated in the pattern of conception (decline during field work season), in the pattern of births, marriage (two maximums, with the prevalence of winter over autumn), and deaths (stronger impact of summer diseases), and in (the already) high age at marriage and relatively modest ratio of remarriages. Considering its historical background (Blato is located on the former border area between Venice and Dubrovnik), this parish may have experienced some of the positive demographic changes from the south somewhat earlier, and according to many determinants, correlated closely with the island of Lastovo, also a borderline island but from the direction of Dubrovnik. In the period 1870-188, Blato experienced the first clear signs of demographic transition: from mortality decline and population growth, to a relatively high marriage age and longer life-span, evidenced in a relatively high age at death. The transition was in its early stage and affected only the mortality of the elderly contingent, while infant mortality still sustained a high rate. A high proportion of extramarital and prenuptial conceptions suggests that ‘test marriage’ may have been customary
