The phenomenon of regional population decline has aroused much attention across the world in recent years, and it is also increasingly obvious in China. Using 1990, 2000 and 2010 population census data, and the national 1% population sample investigation data in 2015, this paper analyzes the evolution trend of regional population decline at the county level in three periods, namely 1990-2000, 2000-2010 and 2010-2015, and identified different evolution types by comparing adjacent periods. We employ a multiple logistic regression model to investigate the underlying driving factors in these processes. The main findings are as follows. (1) The phenomenon of regional population decline became very obvious at the county level, and the percentages of units with population decline in the three periods were all more than 20%. (2) The population decline units expanded significantly from 2000 to 2010, especially in the Northeast region, Sichuan-Guizhou-Chongqing region, and the middle reaches of the Yangtze River, while such units were scattered in the northern part of Jiangsu province and the western part of Fujian province in the Eastern region. (3) The population decline areas presented a trend of slow growth from 2010 to 2015, and only expanded in the Northeast region and Henan province. (4) The factors of economic development level, such as the per capita GDP and the non-agricultural employment ratio, significantly influenced the formation of regional population decline, while the factors of economic development rates, including the growths of per capita GDP and the non-agricultural employment, contributed to the evolution processes of regional population change, and a low economic development rate had been a key factor driving continuous population decline. (5) In addition to economic factors, the natural population growth, including the percentage of the aging population and the birth rate, had an increasing influence on the formation and evolution of regional population decline. According to the above findings, we suggest that the central government should pay more attention to the phenomenon of regional population decline, and take appropriate measures to deal with it, such as promoting the coordinated regional development, adjusting the birth policy to improve the fertility level, and strengthening the planning practice from the perspective of population decline.