Zip code 94591, corresponding to Vallejo in California, has experienced steady population growth over the past decade, with its population increasing from 52,497 in 2010 to 57,475 in 2022. The population density has also risen from 2,774.68 people per square mile in 2010 to 3,037.79 people per square mile in 2022. Given the zip code's size of 18.92 square miles, the estimated number of housing units in 2022, based on the national average household size of 2.61, is approximately 22,021.

The current population density of 3,037.79 people per square mile suggests that the area can be classified as urban. Urban areas are characterized by a mix of multi-story residential buildings, commercial buildings, and high levels of infrastructure and services. The lifestyle in such areas is typically fast-paced, diverse, and culturally rich, suitable for individuals and families who enjoy vibrant city life with extensive public transport, restaurants, theaters, and museums.

Over the past 12 years, the population density in zip code 94591 has increased from a suburban level (1,000 to 3,000 people per square mile) to an urban level (3,000 to 10,000 people per square mile). This shift indicates a growing trend towards urbanization in the area, with an increasing demand for housing, infrastructure, and services.