The level of crowded households shows a mixed picture over time. Occupied housing units with more than one person per room are considered crowded. The rate of crowding declined from 1940 (20 percent) to 1980 (4.5 percent); it rose slightly in 1990 (4.9 percent), and rose again in 2000 (5.7 percent) (see graph).

The rate of severely crowded homes followed a similar trend as crowded homes. Severely crowded homes (those with more than 1.5 persons per room) ranged from a high of 9.0 percent in 1940 to a low of 1.4 percent in 1980. In 2000, 2.7 percent of occupied housing units (2.9 million) were considered severely crowded.

Examples of states with high levels of crowding in 2000 were California and Hawaii, both with a crowding rate of about 15 percent. Severely crowded homes represented 9.1 percent and 7.7 percent, respectively. Maine, Vermont, and West Virginia were examples of states with low levels of crowding, all with only about 1 percent crowding in 2000.

Crowded homes in 1940 were largely concentrated in southern states; this has changed over time. For example, Alabama had a crowding rate of 41 percent in 1940 (twice the national rate), compared with a rate of 13 percent in California, which was below the national rate. The two states had switched places by 1990, and it remained that way in 2000. For Alabama, the crowding rate had dropped to only 2.9 percent in 2000 (below the national rate), whereas for California it was 15 percent (two and a half times the national rate).