The Direct/Delayed Response Project (DDRP) is estimating the number of lakes and streams in three U.S. regions that might become acidic due to current or altered levels of acidic deposition, and the long-term time scales involved. Because of the influence of soils on aquatic chemistry, DDRP acquired data on soils that were mapped, sampled, and analyzed consistent methods across the regions. In the northeastern USA, about 600 soils were identified during mapping of 145 watersheds. Because statistically adequate sampling of every soil was impractical the soils were grouped into 38 sampling classes. Each of these classes was sampled across several watersheds. The properties of soil on specific watersheds (or portions thereof) can be estimated from the regional means and variances of the sampling classes and the percent occurrence of sampling classes on each watershed. The paper describes how the sampling classes for the northeastern USA were developed, the definitions of the classes, and the characteristics of soils within the classes.