The secretary of revenue shall assess the operating property of railroads on the seventh day of July and if the seventh day of July falls on Sunday or on a legal holiday, then the following day, each year. The ownership and valuation of the assessment shall be as of January first each year, and shall be made upon the main line or lines and branches thereof and all sidetracks outside the limits of cities and incorporated towns within the state, separately.
SDCL 10-28-7