Thailand’s 2020 population in the Wikipedia vital-statistics row is 66,186,727. This figure belongs to a registration-based demographic series, alongside recorded births, deaths, natural change, migration change, and fertility—not to a standalone population census total.
The same row lists 569,338 live births and 489,717 deaths, producing a natural increase of 79,621 before migration is considered. Thailand was already experiencing a marked fertility slowdown: its total fertility rate in that row was 1.18 births per woman, well below the approximate replacement level of 2.1.
Readers often confuse the 2020 figure with nearby years. Thailand’s registered population was 66,558,935 in 2019, then fell to 66,186,727 in 2020, partly reflecting the unusually large migration adjustment shown in the table. Later entries decline further as births fall and deaths rise.