  We report recent ground-based photometry of the transiting super-Earth
exoplanet GJ1214b at several wavelengths, including the infrared near 1.25
microns (J-band). We observed a J-band transit with the FLAMINGOS infrared
imager and the 2.1-meter telescope on Kitt Peak, and we observed several
optical transits using a 0.5-meter telescope on Kitt Peak and the 0.36-meter
Universidad de Monterrey Observatory telescope. Our high-precision J-band
observations exploit the brightness of the M-dwarf host star at this infrared
wavelength as compared to the optical, as well as being significantly less
affected by stellar activity and limb darkening. We fit the J-band transit to
obtain an independent determination of the planetary and stellar radii. Our
radius for the planet (2.61^+0.30_-0.11 Earth radii) is in excellent agreement
with the discovery value reported by Charbonneau et al. based on optical data.
We demonstrate that the planetary radius is insensitive to degeneracies in the
fitting process. We use all of our observations to improve the transit
ephemeris, finding P=1.5804043 +/- 0.0000005 days, and T0=2454964.94390 +/-
0.00006 BJD.
