The rendaku morphophonological alternation between voiceless and voiced obstruents in compounds is largely irregular, but it is observed in all Japanese dialects. However, whether dialectal differences in frequency of rendaku has received little attention hitherto. As a first step toward elucidating dialectal differences in the occurrence of rendaku, we examined the rendaku rate of six morphemes in place names from all Japan. The results of our exploratory study indicate that there is no clear geographical pattern in the differences in rendaku frequency, and that it varies between morphemes.