| ca. 900-1500 | Native Americans known as the Tocobaga Indians live in small villages at the northern end of Tampa Bay. |
| 1838 | The name Pithlochascotee River appears on a map. |
| 1859 | Pittitochoscolee, a small settlement located where Port Richey is today, appears on a map. |
| 1863-1864 | Salt is produced at Salt Springs, about one mile north of the Pithlachascotee River. |
| 1877 | A list of Hernando County schools for 1877-78 shows the Anclote, Baillie (Elfers) and Lang (Hudson) schools. |
| 1878 | The Anclote and Hopeville post offices are established. |
| 1882 | Hudson becomes a place name as the Hudson Post Office is established in the home of Isaac Washington Hudson. |
| 1883 | The Gulf Key Post Office is established. (Later names for this area were Argo and Aripeka.) |
| 1884 | Port Richey becomes a place name as Aaron McLaughlin Richey establishes a post office in his home at the mouth of the Pithlachascotee River. (The post office replaced Hopeville post office.) |
| 1887 | Pasco County is formed from the southern part of Hernando County. |
| 1890 | A commercial sponging venture is started at Bailey's Bluff. |
| 1904-1912 | A large sawmill is in operation at Fivay. |
| 1909 | Elfers becomes a place name as the Elfers Post office is established. (The area was previously known as Baillie or the Baillie settlement.) |
| 1912-1913 | The Sass Hotel, the first major structure in Port Richey, is constructed. |
| 1913 | George Sims and a partner purchase the Port Richey Company and begin a major effort to develop the area. |
| 1915 | A post office named New Port Richey is established for the southern part of Port Richey. |
| 1916 | The New Port Richey Post, a short-lived newspaper, is founded. |
| 1918 | The Port Richey Press (later the New Port Richey Press) is founded. |
| 1921 | The First State Bank and the Palms Theater open in New Port Richey. |
| 1921 | A hurricane which makes landfall near Tarpon Springs causes extensive damage. |
| 1922 | The first Chasco Fiesta is held in New Port Richey to raise funds for the Avery Library. |
| 1922 | The first high school in western Pasco County, Gulf High School, opens. |
| 1924 | New Port Richey is incorporated. |
| 1925 | Port Richey and Elfers are incorporated. |
| Mid-1920s | The Florida Land Boom affects western Pasco County, as real estate prices rise and a short period of rapid growth takes place. |
| 1926 | The Meighan Theatre in New Port Richey opens. |
| 1927 | The Hacienda Hotel opens. |
| 1927 | Construction begins on the home of Thomas Meighan, a leading movie star who hopes to persuade other Hollywood entertainment figures to move to New Port Richey. |
| 1931 | First State Bank suspends operation, a victim of the Great Depression. |
| 1933 | Moon Lake Lodge opens. (Much of the Moon Lake Gardens and Dude Ranch is still under construction and does not begin operation until 1937.) |
| 1947 | The Chasco Fiesta is revived. |
| 1949 | A new drawbridge carrying U. S. 19 across the Pithlachsacotee River opens. |
| 1952 | Gulf State Bank opens in New Port Richey. |
| Mid-1960s | A period of rapid, sustained population growth begins, and extends into the 21st century. |
| 1961 | A county government center for the western part of the county opens on Sunset Road in New Port Richey. |
| 1963 | WGUL, the first radio station in New Port Richey, begins broadcasting. |
| 1965 | West Pasco Hospital, the first hospital in western Pasco County, opens. |
| 1971 | Community Hospital opens in New Port Richey. |
| 1976 | Construction is completed on a new campus of Pasco-Hernando Community College in New Port Richey. |
| 1979 | The West Pasco Government Center opens on Little Road in New Port Richey. |
| 1980 | Gulf View Square Mall opens in New Port Richey. |
| 2001 | The Werner-Boyce Salt Springs State Park is dedicated. |
| 2004 | President Bush, campaigning for re-election, speaks in Sims Park in New Port Richey. |