Illinois bundleflower [Desmanthus illinoensts (Mich.) MacMill] is a warm-season perennial legume native to the central USA. Little is known about its forage quality in the upper midwestern USA. Two experiments were established at four Minnesota locations in 2000 to evaluate the effects of N fertilization, maturity at harvest, and residual height of cutting on the acid detergent fiber (ADF), neutral detergent fiber (NDF), crude protein (CP), in vitro true digestibility (IVTD), in vitro dry matter digestibility (IVDMD), and leaf proportion of three Illinois bundleflower (IBF) ecotypes. Whole-herbage forage quality was greatest (P < 0.05) at early flower in mid-July with average ADF, NDF, and CP concentrations of 315, 352, and 180 g kg-1, respectively. Fiber values increased to 412 and 479 g kg-1, respectively, while CP decreased to 129 g kg-1 at late pod in mid-August. Leaf proportion decreased (P < 0.05) from 618 g kg-1 at early flower to 335 g kg-1 at late pod while leaf CP decreased (P < 0.05) from 216 to 147 g kg-1. Whole-herbage IVDMD and IVTD concentrations decreased (P < 0.05) from 470 and 648 g kg-1 at early flower to 390 and 560 g kg-1 at late pod, respectively. Increasing residual cutting height from 15 to 35 cm decreased (P < 0.05) ADF and NDF concentrations by an average of 50 g kg-1 and increased (P < 0.05) IVTD, IVDMD, and CP concentrations by 43, 39, and 20 g kg -1, respectively. Illinois bundleflower can provide good quality summer forage in the upper midwestern USA, but more research is needed to ascertain the implications of its low IVDMD on animal performance.