A lot of sloppy ways have been devised to write place names in genealogy documents. Sometimes, the result is simply unattractive copy. In other cases, the result is ambiguity or utter loss of intelligibility.
The name when it happened.
If they got married in Kanawha County when it was still part of the Commonwealth of Virginia, write
2 PLAC Kanawha County, Virginia, United States of America
Operators of databases intended to help persons find cousins should classify them under their modern equivalent. In this case, the event would be on the page for Kanawha County, West Virginia, United States of America.
Why the word county is so important.
Many counties have the same name as a locality in the same State. To distinguish Merrimack County, New Hampshire from the Town of Merrimack, (which is in Hillsborough County, New Hampshire) it is common to prefix a comma, as follows:
One problem with that is, it is ugly. Further, it doesn't really establish that the writer meant Merrimack County. The reader of a genealogy document has no guarantee that the writer follows the convention of omitting the word county. Consider:
Which is the City of Concord, in Merrimack County, and
Which is part of the Town of Merrimack, New Hampshire.
For localities in Great Britain, on the other hand, the word county is not often used with the county; and to distinguish a county from a locality, the suffix -shire will usually do.
Why the county is so important.
Since the county is often omitted from an address, one might well wonder why it is even necessary to include it in a genealogy document. Consider UNION, OHIO. Brookes Universal Gazetteer (1832/1850) gives dozens of different localities named Union in Ohio. The use of the county name helps the reader to know which Union the writer means, and the county helps a researcher to locate records. If you know town and state but not the county, omit the county:
2 PLAC Nashua, New Hampshire, United States of America
When to omit the designator
Using designators such as City of means a lot of unnecessary work, better dedicated to finding more records. What year did the birth take place? Was it a city or a town? What would you do if the date is uncertain enough that the place might still have been a town, or might have been a city? It is not necessary to use State of Kentucky for events prior to the adoption of the new constitution in 1890, when she became the Commonwealth of Kentucky. It is sufficient to write,
2 PLAC Kentucky, United States of America
In some cases, the designator can help avoid ambiguity:
2 PLAC Nankoda, Republic of Georgia
avoids confusion with Georgia, United States of America.
Only the name of a place
Only the name of a place belongs in the 2 PLAC field. Descriptive words such as probably do not. Explanations belong in the note field. Genealogy software should allow for multiple place names where the source documents available to a researcher do not narrow down the answer better.
For example, the obituary might say she was buried in Saint Marys Cemetery. Some of the graves are in Peabody, Essex County, Massachusetts, United States of America and some of the graves are in Salem, Essex County, Massachusetts, United States of America. If the genealogy software allows for giving both towns, that is much better than the much larger Essex County.
So why not give two places in the 2 PLAC field and combine them with a conjunction?
Peabody and Salem is not the name of a place. Consider:
Bosnia and Herzegovina
King and Queen County, Virginia, United States of America
Newfoundland and Labrador, Canada
Rhode Island and Providence Plantations, United States of America
Saint Kitts and Nevis
São Tomé e Principe
Trinidad and Tobago
Neither should or be used. Consider:
Truth or Consequences, Sierra County, New Mexico, United States of America
Why the country is so important.
Genealogy documents find their way through the internet to readers all over the world. Did you mean Georgia, U.S.A. or the Republic of Georgia? While you may know what you mean, a reader not fluent in your language, in another part of the world, might not.
Using United States for United States of America is just as bad as using Federated States for Federated States of Micronesia or Former Yugoslav Republic for Former Yugoslav Republic of Macedonia.
Include all components even when it is obvious.
2 PLAC Perth, Western Australia, Australia
Dont omit the country just because the name of the State makes it obvious.
Why not to abbreviate.
Abbreviations come and go. They can also mislead. Lincoln, NB can mean Nebraska or New Brunswick, as they both have places named Lincoln. At first, Nebraskas official postal code was NB. There was a time when MS meant Massachusetts.
Only in the cases of U.S.A. and U.S.S.R. is it even necessary to abbreviate. In all other cases, write it all out.
You may be tempted to use Co. for County but it also means Company, and why not just write it out?