What to Know Riverside County was ranked fifth for population growth.

The Census Bureau's analysis covered 3,142 counties and 390 metropolitan areas.

The U.S. Census Bureau released a report Thursday showing Riverside County is not only one of the most populous counties in the country, but one of the fastest growing.

Southwestern states dominated the census bureau's report of county growth for 2017 through 2018 with Los Angeles County leading the list for most populous.

Riverside County was ranked fifth for population growth.

U.S. Census

Figures showed that during the 12-month period ending July 1, 2018, the county's population expanded by 33,534 people, a near 1.5% growth from last year.

The numeric growth was topped again this year by Maricopa County, Arizona, where the population swelled by 81,244 -- the largest growth in the country -- during the same period, according to the Census Bureau.

Maricopa also had extraordinary growth in 2016-2017, with 73,650 people coming into the county.

Riverside County was the only one in California to make the top 10 for largest gainers in the latest report, while Texas had four counties ranked in growth categories.

Among the most populous counties nationally, Riverside ranked 10th for total population as of July 1, 2018, with an estimated 2.45 million people.

That compares with an estimated population of 2.42 million in June 2017. The Riverside-San Bernardino-Ontario metropolitan statistical area ranked eighth among the top 10 highest gaining metro areas in terms of population in 2017-18. The Riverside-San Bernardino-Ontario MSA was at seventh in the prior analysis for 2016-17, according to federal officials.

The metro area's population was about 4.62 million in the 12-month period ending July 1, 2018. In June 2017, the population was around 4.57 million, representing a year-over-year growth rate of roughly 1 percent.

No other metro area in California landed in the largest gaining category. The most populous county was Los Angeles County with just over 10.1 million residents -- a near 300,000 gain from 2010.

The Census Bureau's analysis covered 3,142 counties and 390 metropolitan areas.

Click here to see the data.