The median income of Petroleum County residents was an inflation-adjusted $30,798 per year. Petroleum County had 206 households in 2017, with a population of 453.
The county with the highest median resident income in the state was Fallon County. Fallon County's median income was $32,656 per year after adjusting for inflation – $1,858 more than Petroleum County. It had 1,241 households in 2017 and a population of 2,925.
Glacier County had the lowest annual resident income among counties in Montana, with a median income of only $15,023 per year. That was $15,775 less than the median income in Petroleum County at the time. Glacier County had 4,181 households in 2017 and a population of 13,677.
The table below shows the state's counties ranked by median annual resident earnings in 2017.
| Rank | County | Earnings per resident ($$$) |
|---|---|---|
| 1 | Fallon County | 32,656 |
| 2 | Richland County | 31,620 |
| 3 | Jefferson County | 31,594 |
| 4 | Lewis and Clark County | 31,527 |
| 5 | Petroleum County | 30,798 |
| 6 | Powder River County | 30,385 |
| 7 | Sheridan County | 30,221 |
| 8 | Yellowstone County | 30,112 |
| 9 | Stillwater County | 29,545 |
| 10 | Daniels County | 29,500 |
| 11 | Broadwater County | 29,052 |
| 12 | Prairie County | 28,750 |
| 13 | McCone County | 28,665 |
| 14 | Dawson County | 28,381 |
| 15 | Gallatin County | 28,236 |
| 16 | Park County | 27,860 |
| 17 | Carbon County | 27,574 |
| 18 | Rosebud County | 27,378 |
| 19 | Custer County | 27,088 |
| 20 | Wibaux County | 26,875 |
| 21 | Carter County | 26,799 |
| 22 | Judith Basin County | 26,709 |
| 23 | Cascade County | 26,474 |
| 24 | Flathead County | 26,142 |
| 25 | Sweet Grass County | 25,991 |
| 26 | Valley County | 25,829 |
| 27 | Teton County | 25,193 |
| 28 | Fergus County | 24,807 |
| 29 | Missoula County | 24,766 |
| 30 | Madison County | 24,249 |
| 31 | Wheatland County | 24,081 |
| 32 | Treasure County | 23,917 |
| 33 | Big Horn County | 23,846 |
| 34 | Garfield County | 23,773 |
| 35 | Toole County | 23,755 |
| 36 | Musselshell County | 23,723 |
| 37 | Silver Bow County | 23,687 |
| 38 | Granite County | 23,598 |
| 39 | Hill County | 23,451 |
| 40 | Liberty County | 23,401 |
| 41 | Pondera County | 23,307 |
| 42 | Beaverhead County | 23,053 |
| 43 | Ravalli County | 22,903 |
| 44 | Chouteau County | 22,867 |
| 45 | Lake County | 22,661 |
| 46 | Powell County | 22,629 |
| 47 | Golden Valley County | 22,609 |
| 48 | Deer Lodge County | 22,044 |
| 49 | Phillips County | 21,843 |
| 50 | Roosevelt County | 21,344 |
| 51 | Meagher County | 21,039 |
| 52 | Lincoln County | 20,731 |
| 53 | Sanders County | 19,704 |
| 54 | Blaine County | 19,225 |
| 55 | Mineral County | 18,512 |
| 56 | Glacier County | 15,023 |
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