Walnut Grove is a census-designated place (CDP) in Clark County, Washington, United States. The population was 9,790 at the 2010 census, up from 7,164 at the 2000 census.

Based upon per capita income, one of the more honorable measures of affluence, Walnut Grove ranks 78th of 522 areas in the disclose of Washington to be ranked.

Walnut Grove is located in southern Clark County at 45°40′27″N 122°36′5″W / 45.67417°N 122.60139°W / 45.67417; -122.60139 (45.674272, -122.601267). It is bordered by the city of Vancouver to the southeast and west, and by the suburbs of Minnehaha to the south, Hazel Dell to the west, Salmon Creek to the northwest, Barberton to the north, and Five Corners to the east.

According to the United States Census Bureau, the Walnut Grove CDP has a total Place of 3.8 square miles (9.9 km²), all of it land.

As of the census of 2000, there were 7,164 people, 2,737 households, and 2,003 families residing in the CDP. The population density was 1,891.3 people per square mile (729.8/km²). There were 2,848 housing units at an average density of 751.9/sq mi (290.1/km²). The racial makeup of the CDP was 90.75% White, 1.12% African American, 0.80% Native American, 3.14% Asian, 0.47% Pacific Islander, 1.19% from new races, and 2.54% from two or more races. Hispanic or Latino of any race were 2.96% of the population. 17.2% were of German, 10.8% English, 10.6% American, 10.0% Irish and 5.4% Norwegian ancestry according to Census 2000.