[en] We present a novel plasma diagnostic for measuring local plasma density in reactive-gas plasmas, and depositing plasmas. The diagnostic uses a network analyzer to measure the LC resonance (LCR) frequency of a parallel plate capacitor with inductive leads. The location of the LCR (ω_R) in frequency space is then used as a measure of the plasma dielectric constant bold varepsilon_p between the plates. By properly constructing the LCR probe, ω_R can be tuned such that ω_R >> ω_ce, where ω_ce is the electron-cyclotron frequency. Thus, the probe can be used in plasmas with varying degrees of magnetization while avoiding complications introduced to bold varepsilon_p when ω is comparable to ω_ce. Density measurements from the LCR probe are compared with Langmuir probe measurements in an electron-beam generated plasma in which density varied from 10⁹ to 10¹¹ cm^-3. An axial magnetic field, typically used to confine the electron beam, was varied between 0 to 300 G. The LCR probe showed good agreement with a Langmuir probe across the entire range of magnetic fields.