The average annual population growth rate of Mexico City was the first in the country at 0.2%. The state with the lowest population growth rate over the same period was Michoacán (-0.1%), whereas the states with the highest population growth rates were Quintana Roo (4.7%) and Baja California Sur (3.4%), both of which are two of the least populous states and the last to be admitted to the Union in the 1970s. The average annual net migration rate of Mexico City over the same period was negative and the lowest of all political divisions of Mexico, whereas the states with the highest net migration rate were Quintana Roo (2.7), Baja California (1.8) and Baja California Sur (1.6). While the national annual growth rate was still positive (1.0%) in the early years of the 2000s, the national net migration rate was negative (-4.75/1000 inhabitants), given the former strong flow of immigrants to the United States; an estimated 5.3 million undocumented Mexican immigrants lived in the United States in 2004 and 18.2 million American citizens in the 2000 Census declared having Mexican ancestry. However, as of recent years in the 2010s, the net migration rate reached 0, given the strong economy of Mexico, changes in US Immigration Policy & Enforcement, US Legislative and CFR-8 decisions, plus the (then) slowly recovering US economy, causing many of its former residents to return. The Mexican government projects that the Mexican population will grow to about 123 million by 2042 and then start declining slowly. Assumptions underlying this projection include fertility stabilizing at 1.85 children per woman and continued high net emigration (slowly decreasing from 583,000 in 2005 to 393,000 in 2050).