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We have observed the 158~$\micron$ [CII] and 63~$\micron$ [OI] fine structure lines in a sample of dwarf irregular galaxies with metallicities of 1/6 to 1/2 solar using the Kuiper Airborne Observatory. These data, along with observations of CO$(1-0)$, FIR continuum, and 21 cm HI data, allow us to use photodissociation region models to determine such physical conditions as density, UV field strengths and filling factors in the photodissociated gas. Although these irregular galaxies are typically rich in atomic gas and often have extensive HI halos, the CO emission is relatively meager. We find that the ratio of [CII]/CO(1-0) intensities in these irregular galaxies ranges from 10,000 to 60,000 $-$ about 1.5 to 10 times that observed in our Galaxy. The enhanced [CII] emission is a consequence of the decreased metallicity which results in increased UV penetration depth. This leads to relatively larger photodissociation regions and reduced CO cores.
