| IFFT | Jane | widow | Pearl | Butler | |
| IFFT GEORGE & SONS | dry goods, groceries, &c. | Evansburg | |||
| IMUS | W W | telegraph operator | boards Grand Central | Karns City | |
| IMUS | W W | telegraph operator U P L Co | boards Central hotel | Millerstown | |
| INGALLS | Thomas | oil operator | boards Grand Central | Karns City | |
| INGERSOLL | H D | meat market | Slippery Rock | Millerstown | |
| INGHAUS | Arton | Saxonburg | |||
| INSTONE | William | machinist | Fairview | Karns City | |
| IRELAND | L N | of L N Ireland & Co | residence near Church | Petrolia | |
| IRELAND L N & CO | machinists and blacksmiths | Main | Petrolia | ||
| IRVIN | Alfred A | clerk | Bluff | Butler | |
| IRVIN | Charles | clerk | boards Pearl | Butler | |
| IRVIN | J W | oil producer | boards Lowry house | Butler | |
| IRVIN | John | carriage painter | west Cunningham | Butler | |
| IRVIN | P M | clerk | Bluff | Butler | |
| IRVIN | S P | attorney and real estate agent | Main | Butler | res. Bluff |
| IRVIN | William | physician and druggist | Evansburg | ||
| IRWIN | J T | tobacco and cigars | Main | Fairview | |
| ISLER | Martin | laborer | south McKean | Butler |