Paetulunio fabalis (formerly Villosa fabalis) has experienced a significant reduction in its range and is listed as endangered in both the USA and Canada. Little life history or demographic information exists for the species, but such data are critical for effective conservation. We sampled four streams in the Lake Erie and Ohio River systems of the northeastern USA that support populations of P. fabalis. For each population, we present estimates of total and relative abundance based on catch-per-unit-effort (CPUE) and quadrat sampling, the percentage of recruits, sex-specific shell length, and sex ratios. We collected a total of 572 P. fabalis among the four streams, and the species was the fifth-most abundant overall in mussel assemblages. Recruits (< 20 mm shell length) were present in all streams and made up an average of 19.2% of individuals in CPUE samples and 38.2% in quadrat samples. Shell length varied among streams, but females were consistently smaller than males. Sex ratios did not differ from 1:1 at all streams. The presence of apparently large populations, vigorous recruitment, and balanced sex ratios suggest that all four streams support healthy, stable populations of P. fabalis that warrant protection.