Willowbrook, CA has a population of 22,035 and is the 1,973rd largest city in the United States. The population density is 14,247 per sq mi which is 6031% higher than the California average and 15625% higher than the national average. The median age in Willowbrook is 26 which is approximately 28% lower than the California average of 36. In Willowbrook, 43% of the population over 15 years of age are married, 32% speak English and 67% speak Spanish. 64% of Willowbrook residents were born in California, 4% were born out of state, 1% were born outside of the United States and 31% were foreign born.