This one may have been done already, but I couldn't find anything in a search, so...
"Over the last 15 months, we’ve traveled to every corner of the United States. I’ve now been in 57 states? I think one left to go. Alaska and Hawaii, I was not allowed to go to even though I really wanted to visit, but my staff would not justify it."
Note the POD probably has to be post-1960, or butterfly effects will mean that Obama is never conceived.
Okay, so a total of 60 states? (57 + one left + Alaska + Hawaii)
Canada is a lovely place, but we don't need it to reach 60.
DC granted statehood by the 23rd Amendment in 1961, with only the Mall, the Capitol and the White House remaining the Federal District. The South is incensed the heavily black city is made a state. (Total 51 states.)
Texas splits into 5 states in 1964, to try heading off the 1964 Civil Rights Act in the Senate. It fails to do so, but they split anyway. (Total 55 states.)
In order to balance the extra Democratic states in Texas, on June 4, 1965, the California State Assembly votes to split the state along the Tehachapi Mountains. South California is reliably Republican, of course. (Total 56 states.)
In 1975, amid a budget meltdown, upstate New York State secedes from New York City and Long Island. Upstate New York is now called Hudson. (Total 57 states.)
In 1990, the US Supreme Court in Diro v. Reina, suggested a new state as a means to clarify the legal status of Native American tribal governments. The following year, the state of Native America, a geographically discontinuous conglomeration of 310 recognized Indian reservations is created. (Total 58 states.)
Puerto Rico gains statehood in 1998, by plebiscite, approved by Congress later that same year. (Total 59 states.)
All overseas territories (USVI, Guam, etc.) are organized as a state in 1999. Also eligible are all Americans living overseas or serving outside of their home states for military or diplomatic service. Membership is voluntary, but tax benefits are considerable. The total population is nearly 3 million. The name of the state is "Americans Abroad". (Total 60 states.)