Chromosome numbers are reported for 35 individuals of one of three species of Solidago L. sect. Multiradiatae (Semple) Semple & J. B. Beck from Canada and the United States: S. multiradiata Aiton. Identifications of nearly all vouchers for 101 previously published counts for S. leiocarpa DC., S. multiradiata, and S. spithamaea M. A. Curtis ex A. Gray were confirmed or revised following the delimitation of the section by Semple and Beck (2021). Diploids 2n = 18 occur over much of the range of S. multiradiata with tetraploids occurring in some areas of the range but unknown from others. The two narrowly distributed high Appalachian Mountains species are both polyploid: S. leiocarpa is tetraploid 2n = 36 in New Hampshire, and S. spithamaea is hexaploid 2n = 54 in North Carolina.