Since 2009, the Library Department has lost nearly 300 librarians and other staff members due to budget tightening, amounting to a loss of about 27 percent of its employees.
L.A. Mayor Antonio Villaraigosa and other city officials attended a ceremonial opening Monday morning.
With the Monday closures, library usage and foot traffic went down by some 10 percent according to the city.
In March, 63 percent of voters approved Measure L to boost funding for libraries by increasing the percentage of property tax money the department receives. The measure aims to increase library funding through 2015.
Measure L gave the Library Department about $13 million for the fiscal year. About $1.7 million was set to go toward hiring about 300 part-time librarians and clerical staff.
The resuming Monday hours gives kids and adults a place to study, read at their leisure, do research or search for jobs.
For students like high school sophomore Isis Castillo, the extra day means a lot.
"It's important because we need this place to just hang out, read, broaden our horizons," Castillo said.