The relationship between seeding mixtures and establishment of tallgrass prairie plantings was examined in experimental plots established in 2007. Native grass and wildflower seed mixtures, representing four functional groups (C4 grasses, C3 grasses, nitrogen-fixing species, and late-flowering composites), were sown at five levels of richness/seeding density - 4, 8, 12, 16, and 20 species—in 900-m² plots. Annually, evenness, and total cover and species richness for target (seeded) and non-target (resident) species were measured for the decade from 2007–2016. During the establishment period, eight years received average to above average precipitation; two years experienced drought. Plots seeded with 16 and 20 species achieved 100% target cover by the second year; plots seeded with 12 species had 100% target cover by the fourth year. Plots seeded with 8 or more species had less non-target cover than 4-species plots by the third year, a pattern that persisted for the remainder of the study. Target species richness of plots increased directly with treatment seeding richness, except for the 16- and 20-species treatments that showed no differences in six of the ten years. Non-target species richness varied among treatments beginning in the third year, but did not differ among the 8-, 12-, 16-, and 20-species treatments in the final six years. The results indicate that establishment of prairie-like communities can be hastened by sowing more species at the outset, an important consideration for grassland restoration projects in which diversity and persistence are key goals.