 It was only with the initiation of the Programa Nacional de Solidaridad, in 1988, that the federal government began to install basic services and, ultimately, regularize the tenancy of 77,000 homesteads.During the decades of the 1980s and 1990s, Valle de Chalco expanded dramatically in population; by 1995 the city had 287,073 residents.Growth has since slowed, as undeveloped land becomes less available; in 2005, there were 332,279 residents.