NOAA reported the following yesterday in its April round-up:

The Ohio Valley region had its wettest April on record ... . Illinois, Indiana, Kentucky, Ohio, West Virginia and Pennsylvania each had their wettest April since [at least] 1895. An average of 11.88 inches of precipitation fell across Kentucky, nearly three times its long-term average, breaking the previous record (7.61 inches in 1972) by more than four inches.

Precipitation in inches over the last 30 days. (NOAA)

Joe Romm at Climate Progress discovered an eye-opening summation of rainfall records from the National Climatic Data Center, shown below (which also lists tornado and wildfire records).

(NOAA National Climatic Data Center)

While the rain in the Ohio Valley was likely the top contributor to the historic flooding, heavy snows upstream in the upper Midwest and the associated snow melt, were also a factor in the flooding.