The official total as of July 19 is 15,082 radio stations. This figure doesn't count 824 LPFMs or 6,105 FM translators.
http://hraunfoss.fcc.gov/edocs_public/attachmatch/DOC-315231A1.pdf
FWIW there are also 1,783 TV stations; 6,171 LPTVs & TV translators; and 471 Class A TV stations.
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They didn't start assigning facility IDs with some large number. (look up WRCT (FM) in Pittsburgh) However...
- There are facility IDs for foreign stations. These stations are in the FCC DB, as we're signatory to treaties which require us to not assign stations that would interfere with them. The database contains facility IDs for AM stations throughout the Americas -- all the way down to Argentina & Chile. FM and TV are only listed for Canada & Mexico, and there only for stations close enough to the border to require protection from interference. Still, there are a few thousand such stations.
- Facility IDs are not reused if a station is deleted. (indeed, stations are not removed from the database when they're deleted; they are simply marked as "archive records")
- Facility IDs are assigned to applications. There are for example five facility IDs for 98.9 at Two Rivers, Wisconsin. One of these reflects station WEMP, which holds a construction permit to build on this channel. The other four represent competing applicants who failed to win the frequency.
- There are a few "phantoms" in there. When a TV station requests that its channel assignment be changed, they assign another facility ID for the proposed new channel. I see some (quite a few) IDs that don't seem to represent actual stations or proposals.
- When a LPTV station requests a "Digital Companion Channel", that "DCC" receives a separate facility ID. (strange, as when they did the full-power analog-to-digital transition, a station's DTV facility got the same facility ID as its analog)
- There are some gaps. For example, there is no facility_id 24715, or 34893, or 100982. Among many others.
- Canada notified 1,038 unused TV channel assignments, which dutifully received facility IDs in the FCC DB with the callsign "VACANT". (which ironically would be a valid Canadian callsign

)
As of last night it appears the highest valid facility_id in the table is 190827.