But high land values at two favored locations led the federal government to instead build it 1⁄2 mile (0.80 km) offshore.

It remained in use until the mid-20th century; the construction of the Tappan Zee Bridge on the shoals where it stood and the development of the General Motors Tarrytown Truck Assembly plant on land reclaimed from the river to its east made the light obsolete.

Between it and the developed sections of Tarrytown are the tracks used by Metro-North Railroad's Hudson Line, Amtrak's Empire Service, and CSX freight.

[5] The building itself is a five-story conical structure on a foundation of a stone pier and cast iron caisson,[2] that holds a concrete cylinder which accounts for half the lighthouse's weight, securing it in the river bottom.

But even after the growth in commerce fueled by industrialization during the 19th century, it took a considerable amount of time to find a site for the lighthouse.

It remained in service until the Tappan Zee Bridge's construction made it redundant; since then expansion of the shoreline has also ended its isolation.

The various Native American peoples who lived along its banks used the river European settlers would later name after Henry Hudson, the first of them to explore it, for commerce and trade.

They were aware of the navigational hazards it offered their canoes, and built bonfires on the shores nearest tricky currents and hidden shallows.

[8] Colonists followed them as first sailing ships, then steamships, carried goods and passengers between New York City and the upper limit of navigable waters at Troy.

The former connected the East Coast with the recently settled Midwest; the latter brought anthracite coal from Northeastern Pennsylvania to New York City.

[11] It would be the only one in Westchester County, the only conical steel structure of the seven to have living quarters and the only one on the lower Hudson that could house a keeper and his family.

"The Tarrytown Lighthouse is a familiar sight to the landsman, and its kindly warning rays are always welcomed by mariners", wrote local journalist Isaac De Goff in a 1902 guide to the area.

[6] Apart from routine reinforcement to the riprap and replacement of the dock no changes were made to the lighthouse building itself until the 1940s, when modern sanitary facilities were added.

During the next decade, the original coal-fired steam heating system was replaced with modern forced air, and the sanitary facilities were further upgraded.

[2] The need for the lighthouse was further reduced two years later when the federal government declared all but the hundred feet (30 m) of river bottom around the lighthouse to be surplus property, so that General Motors (GM) could fill in the area between it and the shore in order to expand its Tarrytown Truck Assembly plant, a facility that incorporated the original Stanley Steamer factory built east of the railroad tracks in 1896.

All food had to be obtained by the keeper from land, either by boating to Tarrytown or walking across the ice (a potentially dangerous trip) in winter.

[6] The Morelands have spoken to journalists, including Edward R. Murrow, about family life in a lighthouse that was still, at the time, a half-mile from the nearest land.

During one power outage, Richard Moreland hung an emergency kerosene lamp in the lantern house and rang the fog bell himself.

[6] Other than the isolation, they found the most difficult aspect of living in the lighthouse to be making rectilinear furniture fit against the curved walls.