The frequency of four previously reported far-infrared laser lines have been measured to an accuracy of 100 kHz. These laser lines were measured using a heterodyne system which allowed for more accurate measurement. The four far-infrared laser lines which originated from Formic Acid (HCOOH), O-Deutero-Formic Acid (HCOOD), C-Deutero-Formic Acid (DCOOH), and Methyl Chloride (CH3Cl) were optically pumped by a highly stable, grating-tunable, CO2 laser. Three of the far-infrared laser lines have been measured previously using Fabry-Perot cavities not typicaly known for their high accuracy. The fourth far-infrared laser line had been measured previously by heterodyne methods but under nonoptimal conditions. The difference between the frequencies measured here and the listed frequencies for these laser lines ranged from 0.9 MHz to 3.9 GHz.