54921 is a postalcode and its consensus geometry is derived from uszcta.
{"mz:is_ceased":0,"geom:latitude":44.302395,"wof:name":"54921","counts:names_total":0,"wof:placetype":"postalcode","mz:is_current":1,"wof:hierarchy":[{"continent_id":102191575,"country_id":85633793,"county_id":102081875,"localadmin_id":404492295,"postalcode_id":554728803,"region_id":85688517}],"mz:is_deprecated":0,"lbl:latitude":44.29522,"mz:postal_locality_alt":["Plainfield"],"geom:area":0.022853,"geom:longitude":-89.564474,"wof:id":554728803,"counts:concordances_total":1,"geom:type":"Polygon","wof:lastmodified":1611185061,"wof:belongsto":[102191575,85633793,102081875,404492295,85688517],"wof:concordances":{"gp:id":"12781606"},"wof:repo":"whosonfirst-data-postalcode-us","src:geom":"uszcta","wof:country":"US","counts:names_preferred":0,"gp:parent_id":"12590583","geom:area_square_m":2.02230400692859E8,"wof:tags":[],"counts:names_variant":0,"wof:breaches":[],"edtf:inception":"uuuu","iso:country":"US","counts:names_languages":0,"geom:bbox":"-89.707116,44.213603,-89.405851,44.401952","wof:superseded_by":[],"wof:supersedes":[],"lbl:longitude":-89.559173,"wof:geomhash":"457bc1f49443e4689a67b4cf5bd47835","wof:parent_id":404492295,"wof:placetype_names":["postalcode"],"mz:hierarchy_label":1,"wof:placetype_id":470996387,"edtf:cessation":"uuuu","mz:postal_locality":"Bancroft"}