Switchgrass (Panicum virgatum), a C4 perennial grass native to North America and developed as a sustainable biofuel feedstock, occurs in two ecotypes, lowland and upland, which vary in their architecture as well as their range of adaptation. In this study, we assessed single nucleotide polymorphism (SNP) variation in 372 switchgrass genotypes for nine genes involved in lignin and pectin biosynthesis. STRUCTURE results at K = 3 differentiated the genotypes into three genetic subpopulations that corresponded largely to the previously characterized upland C1 and lowland C2 and C3 subpopulations. Out of the 146 SNPs identified, 19 SNPs were non-synonymous, including two non-conservative and common SNPs in cinnamyl alcohol dehydrogenase (CAD, Chr01N) and p-coumarate3-hydroxylase (C3H, Chr09N), two genes in the lignin biosynthesis pathway. Allele status at seven of the 19 non-synonymous SNPs, including the non-conservative SNP in C3H, was significantly associated with four dry matter traits within subpopulations. Dry matter traits appeared to be mostly dominant and three of them (acid detergent fiber, non-fiber carbohydrate, water-soluble carbohydrates) were the most frequently differentiated traits. In addition, a heterosis effect was detected at the non-conservative SNP in phenylalanine ammonia-lyase (PAL) for neutral detergent fiber. Association analysis revealed the CAD gene on Chr01N, its homoeolog on Chr01K and cinnamate 4-hydroxylase (C4H, Chr03K) as potential candidates associated with dry matter traits. Further analyses are needed to determine whether these candidate genes play a role in switchgrass lignin content and could be exploited to reduce recalcitrance in this bioenergy crop.