In the Sequence-Based format of the Summary File, ZIP Code Tabulation Areas (ZCTAs) are found in the nation file "United States All Geographies Not Tracts Block Groups.zip," starting with the 2007-2011 ACS 5-year estimates. ZCTAs are not available in the state files. More information can be found on the Sequence-Based Summary File format webpage.
In the Table-Based format of the Summary File, the ZCTAs are available in the Geography Files. More information can be found on the Table-Based Summary File webpage.