Gambusia affinis (Western Mosquitofish) is one of the most widespread and invasive freshwater fish. Herein we describe and compare the body size and reproduction of female Western Mosquitofish from 2 small ponds in central Ohio: Wood Duck (WD) and Olde Minnow (OM). This population is one of the most northern populations of Western Mosquitofish to be studied to date. The 2 ponds differed in water temperature (OM > WD), dissolved oxygen (OM » WD), and depth (OM > WD). Body size and body condition of Western Mosquitofish collected was similar in the 2 ponds. Litter size averaged 15.2, increased with female size, and did not differ between ponds. This mean litter size is substantially smaller than that reported for other populations at a similar latitude. Females contained embryos or follicles throughout the study (May–July), but the proportion declined over time, especially in WD. Simultaneous presence of embryos and follicles suggests multiple broods per season, and was more common in OM than in WD. Our results indicate that while females from both ponds were similar in size and had similar litter size, there were potential differences in the frequency of reproduction between the ponds.