For Bohemia and Moravia, the most important source for the demographic in the 17th century are two sets of records. The first one is from 1651, called "A registry list of people by their faith" and the second one is from 1654, "Tax roll assessment". They were collected by the regions and it was used by the government to estimate the tax base due to the disruption of the economy caused by the 30-Years war in the Czech lands. Both sets of records are digitized and the original books are stored in Prague and Brno.

Prior the 30-Years war, the tax, baptistry, and other records were not unified across Bohemia and Moravia, and were not conducted at the same time frame. However, many cities, especially the royal cities and large manors, have records on their estates going back to the 14th century. Prague, Brno, Olomouc, and other large cities had better record keeping; therefore the 1651/1654 records are matched with previous data to estimate the population loss between 1618 and 1648. In areas that experienced significant military operations like northern Bohemia, Moravia, and capital regions around Prague and Brno/Olomouc, they also can deduct the drop in population from lower tax revenues before the war and after, as they were vital for the government in order to fund the war against Sweden or Ottoman Empire. Other areas that were significantly rural, like the highlands, and eastern Moravia, the loss of the population is estimated, sometimes significantly. Also, many records were destroyed in Bohemia as a majority of the cities were captured with the exception of Brno.