| Aero Supply Manufacturing | Corry | PA |
| A.E. Staley Manufacturing | Morrisville | PA |
| Aetna Chemical | Carnegie | PA |
| Aetna Chemical | Oakdale | PA |
| Aetna Explosive | Emporium | PA |
| A. French Spring | Pittsburgh | PA |
| A. Garrison Foundry | Pittsburgh | PA |
| Aggregates Equipment | Leola | PA |
| A. Guckenheimer & Brothers | Freeport | PA |
| A.G. Vento Plumbing | Greenville | PA |
| A Hill | Erie | PA |
| A. Hirsch Air | Philadelphia | PA |
| A.H. Wirz | Chester | PA |
| Aiken Medical Building | Pittsburgh | PA |
| Airco | Butler | PA |
| Airmaster | Philadelphia | PA |
| Air Products | Johnstown | PA |
| Air Products | Emmaus | PA |
| Air Products | Allentown | PA |
| Air Products | Pittsburgh | PA |
| Air Reduction | Bethlehem | PA |
| Air Reduction | Butler | PA |
| Air Reduction | Enola | PA |
| A.I.W. Frank | Exton | PA |
| Ajax Forge | Philadelphia | PA |
| Ajax Forge | Corry | PA |
| A.J. Cameron | Philadelphia | PA |
| A.J. Haws & Sons | Johnstown | PA |
| A.K. Garrett | Philadelphia | PA |
| Alamogordo Lumber | Scranton | PA |
| Alan Wood Iron & Steel | Conshohocken | PA |
| Alan Wood Iron & Steel | Ivy Rock | PA |
| Alan Wood Iron & Steel | Philadelphia | PA |
| Alan Wood Iron & Steel | Norristown | PA |
| Alan Wood Iron & Steel | Swedeland | PA |
| Albright Coal | Pottsville | PA |
| Albright Coal | Llewellyn | PA |
| Alcania Tin Plate | Avonmore | PA |
| Alcoa Corporation | New Kensington | PA |
| Alcoa Corporation | Cressona | PA |
| Alcoa Research Laboratories | Pittsburgh | PA |
| Alcoa Research Laboratories | New Kensington | PA |
| Alcoa Technical Center | Alcoa Center | PA |
| Alden Coal | Alden | PA |
| Aldon Rug Mills | Lenni | PA |
| Alexander Brothers | Philadelphia | PA |
| Alexander Good Elementary School | York | PA |
| Alexander Plumbing | Pittsburgh | PA |
| Alex Crow & Son | Philadelphia | PA |
| Algonquin Chemical | Hamburg | PA |
