Wills: Oldest existent will in Maryland is from 1635. Extracts of Wills through 1777 have been published. (There are a few errors of course, but overall very useful). Wills, in additon to naming heirs provide information on tracts of land owned, sometime a chain of title, neighbors, and the witnesses. The actual wills and copies are available at MSA. Wills and Probate were Providence, not county, level records up until 1777.
Inventories and Accounts of the Perrogative Courts from 1674 to 1777 have be extracted and published. As sterling was in short supply, IOUs seem to have been commonly used. These extracts will often list 100s of persons in debt or (usually fewer) receiving payments from an estate along with limited information on heirs. It will commonly have the executrix of estate showing her new husband. Copies of the actual inventories are available at the Maryland State Archives (MSA). It is very interesting to see what personality our ancestors owned.
Land Grants. A signficant resource in searching early Marylanders. Up until 1680, the proprietorship granted 50 acres for each person transported into Maryland to reside. Thus most people coming into Maryland or transporting others into Maryland took advantage and requested warrants for land, naming the individuals transported. In some cases, these were for family, often for indentured servants, and in some cases it seems for business deals and family/religious groups. Thus a significant number of all persons coming into MD in that era can be found named in these requests for land warrants. This information has been extracted and an index of names, dates of warrants (which may be later than the date the person entered MD), the person claiming the warrant, and cites to the liber/folio of the records. It is available in "The Early Settlers of Maryland" by Gus Skordas. Land grants and patents continued to be issued after the headright system was phased out. In some cases landowners had resurveys done to increase their holdings by incorporating any adjacent vacant land. I have seen land patents and surveys as late as the 1850s.
Land Records. Baltimore Co land records are in existance from 1665 on. These land records often will have Grantor and his wife named. Some records can contain very useful genealogical material, including references to now non-existant wills, listing of heirs, and tracking the title to tracts of land. Land could pass through several generations in a family without any deeds, so tracking tracts of land is one method to help identify a family.
Court and Legislative Records. Records of court cases and actions of the legislature can sometimes provide early genealogical material.
Church Records. In June of 1692, the Church of England (Episcopal) Church was designated as the established church of Maryland. One of the responsibilites of each Parish was to maintain a register of births, deaths, and marriages in the Parish. Baltimore County originally had three parishs, St. Pauls, St. Johns, and St. Georges. The existant records for St. Pauls Parish seem to start about 1717, Records for St Johns and St. Georges start at 1696. In additon the Quaker Meetings kept their own set of minutes, which includes marriages. Additional Parishs were erected in the 1700s to serve the increasing population and provide for easier access (shorter trips). These include St Thomas Parish (est. 1732) at Garrison Forest, and St James Parish (est. 1750) at Monkton. Since many early settlers of Baltimore Co came from Anne Arundel County, it is often useful to check the Anne Arundel Co. parish records or the Quaker meeting records.
Tax lists exist for various years. About the earliest are for 1699 to 1704 for Baltimore Co.
Militia memebership lists, List of petitioners to move the Courthouse from Joppa Town to Baltimore Town in 1768, and other misc. lists of persons signing documents or belonging to organizations have been published in various books and articles.