Where did Jonathan Parker die in 1788? Probate records are kept at the county level and some of the records are on-line.
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The Federal Government does not ordinarily create or maintain probate records. Such records are made and kept by the local government (County/Township/Municipality) rather than the National Archives. Considering the age of the probate record you are trying to find, that record is more than likely in possession by the State Archives that Jonathan Parker died in. We would suggest that you contact the appropriate institution, a list of which can be found by visiting this link below:
We also suggest searching substitute record sources such as probate records, church records, and newspaper records that may uncover more information about your ancestor. For more information on conducting genealogical research within our records, please visit the following link:
We hope this information is helpful and best of luck with your research!