In 4 metro areas, incomes dropped by 17%, making them the top 10 U.S. cities where salaries are shrinking fastest.

Unfortunately, despite the national increase in median household income by 4% between 2022 and 2023, as per the latest U.S. Census Bureau data, incomes weren't growing everywhere.

In 2023, the median household income in Marysville, Washington, decreased by nearly 18% compared to the previous year, from $104,433 to $85,708, according to a SmartAsset analysis of Census Bureau data. This was the largest annual decline in median income among over 600 U.S. cities with populations of at least 65,000, SmartAsset reports.

In three cities - Champaign, Illinois; Madera, California; and Baton Rouge, Louisiana - median incomes decreased by at least 17%.

According to SmartAsset, these are the cities that experienced the most significant drops in median household income from 2022 to 2023.

Why incomes are falling in Marysville

The decline in median household income in Marysville can be attributed to the departure of a significant number of high-earners. According to SmartAsset, the percentage of local households earning at least $100,000 decreased from 54% in 2022 to approximately 41% in 2023. However, the percentage of households earning at least $200,000 increased slightly.

"According to SmartAsset's director of economic analysis, Jaclyn DeJohn, high-earners often have the ability to depart and explore new opportunities, which can significantly impact the earnings of a specific community."

Although Marysville's earnings have decreased, its median income of $85,708 is still higher than the national median of $80,610.

According to the Massachusetts Institute of Technology's living wage calculator, an individual earning that much in Marysville could afford the basics, including rent, food, health care, and transportation, given that it takes a $61,545 annual salary for an individual without kids to live comfortably in Snohomish County, Washington.

In 2023, the median household income in Washington state was $93,440, with higher-income cities like Seattle and Bellevue contributing to this figure, with median incomes exceeding $100,000.

In metropolitan areas, where salaries are already below the national average, incomes are further decreasing.

Despite a similar decline in median incomes in Champaign, Madera, and Baton Rouge, these cities' residents were already earning less than the national average in 2022. In 2023, their median household income fell below $60,000.

The decline in the working age population in Champaign and Baton Rouge between 2022 and 2023, as per Census Bureau data, may be partly due to age, DeJohn says.

"This suggests that individuals may be leaving the workforce or accepting lower incomes for greater flexibility to care for their children or families, or that workers may retire and earn less than they did during their peak working years."

In contrast to other regions in the country, residents in the Midwest and South generally earn less, with Louisiana having the second-lowest median household income at $57,650.

While Illinois and California are known for their higher median household incomes, Champaign and Madera, located far from major cities, have lower incomes. For instance, Illinois' median household income is $87,820, but this is largely due to Chicago's metro area, where the median income is $74,474, almost $30,000 higher than what is earned in Champaign.

To earn extra money online, sign up for CNBC's course on passive income streams, starting tips, and real-life success stories.

Sign up for CNBC Make It's newsletter to receive expert advice on work, money, and life.