Unlike the rest of the Phoenix metropolitan area, population density in central Phoenix dropped during the 1970s and 1980s. The primary cause was a decrease in the number of housing units. Rising vacancy rates contributed, but the increase in vacancy rates was similar to that of the entire metropolitan area. Between 1990 and 1995, population density rose in central Phoenix. A sharp decline in vacancy rates was a major factor in the turnaround, though the vacancy rate decline only matched that of the entire metro area. Another major factor in the increase in density was the rising number of people residing in prisons, homeless shelters, or on the streets.

The Phoenix metropolitan area is new by national standards, having developed primarily since World War II and particularly since 1970. However, settlement patterns were established in the 1800s, in part due to topographic features such as water courses and mountains. The war effort during World War II stimulated the growth of the Valley. After the war, a combination of events led to much faster growth. These included the desire of ex-servicemen stationed in the area during the war to return; improvements in air conditioning; charter government in Phoenix, which allowed a small pro-growth business group to gain power; and
aerospace and electronics firms siting facilities, in part because of the federal government’s designation of Fort Huachuca as the principal proving ground for electronic defense equipment. The modern period began around 1970, when a maturing metro area coincided with the baby-boom generation reaching adulthood. The result was even more rapid growth that has continued to the current time. Rapid growth of the Phoenix metro area is expected to continue for at least the next 50 years. Land and water availability should not restrict growth until after the current population of nearly three million exceeds seven million in 2050.

The war on poverty during the 1960s succeeded, cutting the national poverty rate in half by the early 1970s. Since then, however, the poverty rate of Americans under the age of 65 has increased. The poverty rate has climbed particularly among children; compared to an average of 15.5 percent during the 1971-to-1975 economic cycle, the poverty rate in each of the three cycles since 1982 averaged between 18 percent and 21 percent. One-in-five children lives in poverty and Arizona has consistently experienced higher poverty rates than the national average for all age groups except seniors.