Maricopa County, AZ (FIPS 04013): Phoenix Area Profile

Maricopa County, Arizona (FIPS 04013) is the fourth most populous county in the United States and consistently ranks among the fastest-growing large counties in the country. Home to Phoenix, Scottsdale, Tempe, Mesa, Chandler, and Glendale, Maricopa County is essentially a county-sized metro — it is the sole major county of the Phoenix-Mesa-Chandler MSA (38060), which makes it unusual among large metros where the core city represents a smaller share of total county population.

The FIPS code 04013 breaks down as: state 04 (Arizona) + county 013. Maricopa County's rapid population growth — driven by in-migration from California and across the Sunbelt — makes it a frequent subject of population estimate validation research. The Census Bureau's Population Estimates Program (PEP) publishes annual county estimates, and for fast-growing counties like Maricopa, the estimates can lag actual growth significantly between decennial census years.

In federal environmental data, Maricopa County is notable for air quality challenges — the Phoenix metro has historically exceeded EPA standards for ozone and fine particulate matter (PM2.5), partly due to vehicle emissions and dust from construction and natural desert sources. AQS monitoring data for Maricopa (04013) shows the county's air quality trajectory over decades. FEMA flood data is also relevant — despite being in a desert, Phoenix area waterways create significant flood risk, and NFIP data shows meaningful policy volume.

In BLS QCEW data, Maricopa County's employment growth in construction, leisure and hospitality, and financial services reflects the growth economy. The county's median age skews young relative to national averages, and in-migration patterns are well-documented in IRS migration data, which tracks county-to-county flows using FIPS codes. Browse the full Maricopa County profile or explore Arizona's county list to see the context of this county within the state.