The article follows Irena Gieysztor’s call encouraging scholars to compare nearly simultaneous registers of taxes — the 1661 chimney tax and the 1662 poll tax — compiled throughout the Kingdom of Poland. Such comparisons on a microscale — for individual villages of parishes — would make it possible to determine the reliability of both registers and, consequently, their usefulness for historians studying demography. The present author analyses these two registers from a village parish of Krzynowłoga Mała (Ciechanów region), which had a high percentage of petty nobility. The chimney tax (levied on buildings) was paid in this parish by no fewer than 154 noblemen — among them, only 7 paid the tax on behalf of peasants, while the others paid it for themselves (petty nobility). There were 204 nresidential buildings, including manor houses and the vicarage, in the parish. The poll tax (levied on people, with the exception of the elderly, beggars, cripples and children under the age of 10), shows the peasant population as a collective and the nobility — as individual households, of which there were as many as 191. In total, there were 954 taxed individuals — 513 noblemen, 22 craftsmen, 419 peasants and servants. In addition, the parish register also included about 10 persons living in the vicarage (the tax paid in separate registers for the clergy). Taking into account an upward adjustment of 27%, there were 1320 people living in the parish at the time. There are no surviving comparative sources. A comparison of both tax registers has enabled the author to determine the number of people in one peasant household — 6.3 (8.7 after upward adjustment). The poll tax register is much more reliable and complete than the chimney tax register, because it shows various social groups. In the poll tax register we have 184 petty nobility households, while the chimney tax was paid by only 146 of such noblemen.