Dear Ms. Clark,
Thank you for posting your request on History Hub!
The Federal Government does not ordinarily create or maintain birth, death, marriage or divorce records. Such records are made and kept by State and local governments rather than the National Archives. According to the Genealogical Records at the Library of Virginia, few marriage records prior to 1730 survive in parish registers or county court record books, even though marriage bonds were required by law as early as March 1661. As a rule, these records list only names of the bride and groom, the names of the security, and the date issued. The names of parents and the ages of the couple seldom are found in pre-1853 marriage records.
We searched Ancestry and located All Virginia Marriage Records 1700-1850 for William Smith; and All Marriage & Divorce results for Ann Isham. There may be a fee for using Ancestry. Instead, you may view these records online at one NARA's facilities for free via a NARA PC. For the nearest NARA location, please consult our web page at https://www.archives.gov/locations/. Also, some of the images from Ancestry are available for free on Family Search at https://www.familysearch.org/en/.
We hope this is helpful. Best of luck with your research!