The absolute populations of the vibrational levels ν = 0, 1, 3 and 6 of the state of molecular nitrogen produced in a low pressure inductively coupled plasma have been determined as a function of plasma operating conditions. The measurements were conducted using diode laser-based cavity enhanced absorption spectroscopy on a selection of vibrational bands within the strong first positive system, , and calibrated using cavity ring-down spectroscopy. At 25 mTorr and 200 W power applied to the discharge we find the populations of the ν = 0, 1, 3 and 6 levels to be (1.31 ± 0.16) × 1011 cm−3, (8.44± 1.01) × 1010 cm−3, (2.83 ± 0.34) × 1010 cm−3 and (5.27 ± 0.63) × 109 cm−3, respectively, corresponding to a vibrational temperature of 3600 ± 150 K. The vibrational temperature of the A-state was determined to lie in the range 2900–3700 K for the operating conditions employed. The translational and rotational temperatures of each vibrational state probed were considerably colder (in the range 300–500 K) and show the translational and rotational modes to be equilibrated. In addition, we present the observation of the ) molecular ion in its vibrational ground state using both cavity enhanced absorption spectroscopy and the same technique in combination with wavelength modulation spectroscopy. At 10 mTorr and 400 W we measure a translational temperature of (431 ± 80) K, which is the same as that for the A-state under the same conditions, and estimate the total population in ν = 0 to be (1.26 ± 0.15) × 109 molecules cm−3. The combination of cavity enhanced and wavelength modulation methods is found to improve the sensitivity by approximately an order of magnitude in a plasma environment.