The median income of St. Mary's County residents was an inflation-adjusted $40,735 per year. St. Mary's County had 39,276 households in 2017, with a population of 110,979.
The county with the highest median resident income in the state was Howard County. Howard County's median income was $53,458 per year after adjusting for inflation – $12,723 more than St. Mary's County. It had 111,337 households in 2017 and a population of 312,495.
Somerset County had the lowest annual resident income among counties in Maryland, with a median income of only $19,650 per year. That was $21,085 less than the median income in St. Mary's County at the time. Somerset County had 8,362 households in 2017 and a population of 25,801.
The table below shows the state's counties ranked by median annual resident earnings in 2017.
| Rank | County | Earnings per resident ($$$) |
|---|---|---|
| 1 | Howard County | 53,458 |
| 2 | Montgomery County | 45,904 |
| 3 | Charles County | 45,306 |
| 4 | Calvert County | 44,591 |
| 5 | Anne Arundel County | 42,069 |
| 6 | St. Mary's County | 40,735 |
| 7 | Frederick County | 40,183 |
| 8 | Carroll County | 39,902 |
| 9 | Harford County | 38,965 |
| 10 | Queen Anne's County | 38,525 |
| 11 | Prince George's County | 37,102 |
| 12 | Baltimore County | 36,370 |
| 13 | Cecil County | 34,576 |
| 14 | Talbot County | 32,527 |
| 15 | Worcester County | 29,350 |
| 16 | Washington County | 28,804 |
| 17 | Dorchester County | 27,226 |
| 18 | Wicomico County | 26,359 |
| 19 | Caroline County | 26,314 |
| 20 | Kent County | 26,182 |
| 21 | Garrett County | 24,048 |
| 22 | Allegany County | 22,345 |
| 23 | Somerset County | 19,650 |
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