If our fire company is not voluteer anymore, will the county own the building?

No. Under the terms of OPA's long-standing contract (unchanged), if the fire department is ever dissolved all property, equipment, etc. becomes the property of OPA.

Also, OPA is required to provide fire protection (not EMS) by virtue of the Declarations of Restrictions and/or the Articles of Incorporation. If the volunteers disappear then OPA would have choices. It could contract with Showell Fire Department, for example, or it could hire full time fire fighters, just as it has done to meet a  similar DR requirement saying OPA must provide police protection. That requirement has sure come a long way from the minimal way to comply with the DRs via a couple of contract security guards.

You are probably confused relative to the dissolution of OPA itself. In that case I believe the county would take over all OPA common property.