According to data published by Public Health England today, figures rose from 428,255 in 2011 to 448,422 in 2012.
PHE said the increase was mostly due to improved data collection. However, it warned that the continuing high rates of STI in England "suggest too many people are still putting themselves at risk through unsafe sex".
It said this was particularly the case among young adults and men who have sex with men (MSM).
With 206,912 new diagnoses last year, chlamydia remains the most common STI diagnosis. New cases of gonorrhoea rose 21% overall, from 21,024 in 2011 to 25,525 in 2012. The MSM community saw a 37% increase in gonorrhoea diagnoses.
There were also significant numbers of diagnoses of genital warts (73,893, or 16%) and genital herpes (32,021, or 7%).
Under-25s experienced the highest rates of STI, accounting for 64% of chlamydia and 54% of genital warts diagnoses among heterosexuals in 2012.
Dr Gwenda Hughes, PHE head of STI surveillance, said there was a need to invest in sexual health awareness programmes and testing.
"There have been significant improvements in screening in recent years, particularly for gonorrhoea and chlamydia among young adults and men who have sex with men, so we are diagnosing and treating more infections than ever before," she said.
"However, these data show too many people are continuing to have unsafe sex, put themselves at risk of STIs and the serious consequences associated with infection, including infertility. Ongoing investment in programmes to increase sexual health awareness, condom use and testing, particularly for groups at most risk, is vital.
"We must also ensure chlamydia screening remains widely available. Local authorities should continue to integrate chlamydia screening into broader health services for young adults. This will also help this age group develop positive relationships with services, enabling them to develop and maintain good sexual health throughout their lives."
Professor Kevin Fenton, PHE director of health and wellbeing, also encouraged regular STI screening.
"Getting screened for HIV and STIs can lead to early diagnosis and treatment, as often these infections have no symptoms. In addition, reducing the number of sexual partners and avoiding overlapping sexual relationships can reduce the risk of being infected with an STI," he said.