Located in south central Montana, Yellowstone County is Montana's most populous with an estimated 144,797 residents in 2009, according to the Montana Department of Commerce.
Billings, the county seat, is the state's largest city with an estimated population of 105,845 (2009) and is a major retail and wholesale trade, financial, energy, transportation and medical center. According to the Montana Almanac, by authors Andrea Merrill and Judy Jacobson, the county was established in 1883. The Yellowstone River, the authors say, was called by early French trappers, Roche Jaune for "yellow rock." Pompeys Pillar, an area landmark, was originally called Pompy's Tower by Captain William Clark. The authors add he named it after Sacajawea's son Baptiste, whom he called "Little Pomp." Billings was named for lawyer, philanthropist and former Northern Pacific Railroad President Frederick Billings.
The county is 2,666 square miles in area; 2,635 square miles in land area and 31 miles in inland water area. According to the Montana Department. of Commerce, median income for Yellowstone County households is an estimated $40,627.
County residents experience the four distinct seasons. According to the National Weather Service, the average daily high in January is 32 degrees farenheit with an average low of 15 degrees above zero and average snowfall of 10.9 inches. The average daily high in July is 85 degrees farenheit, with an average low of 58 degrees, and average precipitation of 1.28 inches. The average last frost date is May 14th, with an annual growing season of approximately 131 days. The annual average wind for Billings is 11mph from the southwest.