Boulder Creek, CA has a population of 4,442 and is the 6,974th largest city in the United States. The population density is 591 per sq mi which is 154% higher than the California average and 553% higher than the national average. The median age in Boulder Creek is 47 which is approximately 31% higher than the California average of 36. In Boulder Creek, 54% of the population over 15 years of age are married, 93% speak English and 5% speak Spanish. 65% of Boulder Creek residents were born in California, 29% were born out of state, 3% were born outside of the United States and 3% were foreign born.