According to the United States Census Bureau, the CDP has a total area of 15.9 square miles (41.2 km2), of which, 15.3square miles (39.6 km2) of it is land and 0.6 square miles (1.6 km2) of it is water. The total area is 3.78% water. The military base is, as previously stated, much larger than the CDP defined by the Census Bureau.
Fort Lewis’ terrain is primarily a mixture of dense conifer woods and open Puget prairie-garry oak woodlands. Invasive Scotch Broom has taken over many areas. The landscape is very rocky from glacial meltwater deposits. Poison oak is found in the training areas. Canada Thistle grows thickly in some areas. All trees are to be left standing; post policy prohibits cutting or trimming them.
The temperatures during summer vary from the mid 40s at night to the mid 70s during the day, occasionally peaking over 90 °F (32 °C). Although July and August are the driest months.
Fort Lewis, due to its size and reserved land, serves as an important habitat for amphibian development and study.
The census-designated place (CDP) Fort Lewis is located within the installation’s area. As of the 2000 census, the CDP, which includes the most densely populated part of the base, had a total population of 19,089.
As of the census of 2000, there were 19,089 people, 3,476 households, and 3,399 families residing on the base. The population density was 1,248.5 people per square mile (482.0/km2). There were 3,560 housing units at an average density of 232.8 per square mile (89.9/km2).
There were 3,476 households, out of which 85.8% had children under the age of 18 living with them, 89.3% were married couples living together, 6.6% had a female householder with no husband present, and 2.2% were non-families. Of all households 2.0% were made up of individuals, and 0.0% had someone living alone who was 65 years of age or older. The average household size was 3.75 and the average family size was 3.78.
The age distribution was 32.1% under the age of 18, 28.0% from 18 to 24, 37.5% from 25 to 44, 2.0% from 45 to 64, and 0.4% who were 65 years of age or older. The median age was 22 years. For every 100 females, there were 168.3 males. For every 100 females age 18 and over, there were 212.5 males. All these statistics were typical for military bases.
The median income for a household on the base was $32,384, and the median income for a family was $32,251. Males had a median income of $20,878 versus $20,086 for females. The per capita income for the base was $12,865. 8.2% of the population and 7.1% of families were below the poverty line. Out of the total population, 10.7% of those under the age of 18 and 0.0% of those 65 and older were living below the poverty line. Source: (Wikipedia)