We present results from multi-band near-IR (J, H, and K) imaging of twelve BL Lac objects (z=0.055 to 0.774 for the 11/12 with well-determined redshifts) obtained with the du Pont 2.5m f/7.5 telescope at the Las Campanas Observatory. These AGN are a subset of the much larger BL Lac sample surveyed with HST, mostly in the R band. All twelve BL Lacs were imaged in K band, five in J, and two in H. We extracted one-dimensional profiles from each image and fitted them with a PSF plus de Vaucouleurs r1/4 galaxy model. We resolved eight host galaxies clearly, three are marginally resolved, and one is unresolved. The median K band galaxy magnitude is 14.3. We present the images, the near-IR colors and the integrated K-R colors of the host galaxies, which are consistent with those expected from old stellar populations at the BL Lac redshifts. We thank the STScI 2000 Summer Student Program and its coordinators. Support for this work was provided by NASA through grant number GO-07893.01-96A from the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.