Łódź offers direct rail connections with major Polish cities, including Warsaw (20 direct connections a day on working days, 14 – at weekends, the trip lasts about 1.5 hrs.), Kraków, Wrocław and Gdańsk. The current timetable is available here. Łódź Agglomeration Railway that connects Łódź with other cities and towns in the province, such as Sieradz, Zduńska Wola, Łowicz, Kutno, Zgierz, Koluszki and Skierniewice, has been available for several years.
You should know that there are several stations in Łódź, including Łódź Fabryczna –– the largest and most modern underground railway station, which has been newly commissioned after a thorough reconstruction and is located in the New Centre of Łódź, as well as and the Łódź Kaliska station. There are plans to connect both stations by constructing a cross-city railway tunnel (in 2022).