Early in the 20th century, elevated and subway trains allowed masses of workers to commute to Manhattan jobs from Queens and eastern Brooklyn, which offered cheaper and larger housing but were far beyond reasonable walking distance. Immigrants spilling over from New York City made comfortable lives on Long Island. The immigration waves of Southern and Eastern Europe have been pivotal in creating the diversity on Long Island that many other American regions lack. These immigrations are reflected in the large Irish American, Italian American and Jewish-American populations. Typically the immigrants lived in the city first or the more urban western parts of the island, and their children and grandchildren moved further east. Late-20th-century immigrants, by contrast, often settled directly in Nassau County and other suburban areas.
When racing was banned on public roads, one of the Vanderbilts opened the Long Island Motor Parkway in 1908 from Kissena (Queens) to Lake Ronkonkoma. This limited access motor highway was one of the first in the world.
In the 1920s and 1930s, suburbanization reached beyond the western end of the island, and Long Island began the transformation from backwoods and farms to the paradigm of the American suburb. Under its president Robert Moses, the Long Island State Park Commission spanned the island with parkways and state parks. Jones Beach was the most famous, “the crown jewel in Moses’ State Park System”. Long Island quickly became New York City’s retreat – with millions of people going to and from the city to the new state parks. In time, development started to follow the parkways and the railroad lines, with commuter towns springing up first along the railroad, then the roadways: the Southern State Parkway, the Northern State Parkway, and, from the 1960s on, the Long Island Expressway.
After World War II, Long Island’s population skyrocketed, mostly in Nassau County and western Suffolk County. People who worked and lived in New York City moved out to Long Island in the new developments built during the post-war boom. The most famous post-war development was the town of Levittown. Positioned along the Wantagh Parkway and near Southern State Parkway, in the area formerly known as Island Trees, Levittown became the first place where a developer built numerous adjacent houses in one subdivision, providing great opportunity for GIs’ returning home to build families.
After the success of Levittown, other areas modeled what some people criticize as “suburban sprawl”, and Nassau County became more densely populated than its eastern counterpart, Suffolk County. In the late 1960s, areas in Suffolk County, such as Deer Park and Commack, also saw rapid development. Driving out east along routes such as New York Route 27 (Sunrise Highway) along the South Shore or on the North Shore along New York State Route 25 (Jericho Turnpike) or New York State Route 25A, houses and buildings start to spread out, even turning back to the potato and sod farms that once were East of and including towns such as Mount Sinai. (Although Development is Spreading Further East).