In 1876 Mr. Guernsey was instructed by the commissioners of the new county of Columbia--F. G. Frary, G. T. Pollard of Huntsville and E. Oliver of Pomeroy--to call a special election for the purpose of choosing county officers. Mr. Guernsey was elected county treasurer for one year and at the first biennial election was chosen for a full term at a salary of three hundred dollars per year, the officers being required to serve at a "moderate salary" inasmuch as this was an infant county. In 1878 he was chosen to represent his district in the territorial legislature and on the 31st of July, 1880, he succeeded L. F. A. Shaw in the office of deputy collector of internal revenue under Major James R. Hayden. He occupied that position for three years and then surrendered the office to H. W. Fairweather. On the 4th of May, 1884, Mr. Guernsey entered the Columbia National Bank of Dayton as cashier and had complete charge of the bank's affairs through the following sixteen years, at which time his brother, F. W. Guernsey, became cashier, while D. C. Guernsey was made vice president and manager of the institution. He successfully carried the bank through the panic of 1893, although he closed one Saturday night with but five hundred and fifty dollars in the bank. However, he most carefully safeguarded the interests of the institution and managed to weather the financial storm which swept over the entire country in that year. He remained in his official capacity with the bank until 1900, when he retired, the institution at that time having deposits of three hundred and seventy-four thousand dollars. He then turned his attention to the real estate, insurance and loan business in Dayton and in 1904 he took charge of a mining camp on the Omnaha in Willowa county, Oregon, for the Eureka Mining Company, his position being that of managing director. While there he built the wagon road down Deer creek from Dobbins Cabin to Snake river. He occupied the position of director of the mining camp for two years, after which he returned to Dayton and through the succeeding two years gave his attention to the real estate and insurance business. In 1908 he removed to Starbuck to assist in straightening out the affairs of the Bank of Starbuck, of which institution he was made cashier, occupying that position for a period of two and a half years. He then resigned and established his present business, with which he has since been prominently identified, being today one of the foremost real estate, loan and insurance agents in this part of the state. One of the local papers said: "D. C. Guernsey has been a most important factor in the development of Columbia county and the moulding of civilized life in the great state of Washington. During the early history of Columbia county, hardly a business transaction was carried through or a public enterprise launched that was not inspired by the brain or fostered by the public-spiritedness of Mr. Guernsey." He helped to organize and was the first president of the Dayton Electric Light Company and built many of the buildings in that city in the block in which the Columbia National Bank is located. He organized the Dayton Hotel Company, which built the hotel, and was its president for several years.