Census records for St. Mary's County (and some for Charles County) are available in our Research Library. St Mary's County census records are available in book form for these years: 1790 thru 1820, 1840 thru 1880, 1900 Thru 1930; 1940 Index is available on CD. Charles County census records are available in book form for these years: 1790 thru 1880. They are also available for sale in our bookstore. These records have been transcribed by volunteers and may be easier to work from than images of the original records. However, original images are available on-line at FamilySearch (free) and Ancestry (paid subscription required)
Census Enumeration District Maps SMCHS publication identifying election district areas by census year.