There are many areas that have a "Longwood" mailing address that are not actually in the incorporated City limits of Longwood. If you are in an unincorporated area, you will actually do your permitting through Seminole County.
One way you can check is by searching your address or parcel number at the Seminole County Property Appraiser's GIS site.
A quick shorthand is that any property located west of I-4, including the Wekiwa Springs and Jamestown areas, or any property with a 32779 zip code, are not located within the City of Longwood.