To register to vote online:
https://www.pavoterservices.state.pa.us/Pages/VoterRegistrationApplication.aspx
To download and print a voter registration form:
https://www.lehighcounty.org/Portals/0/PDF/Voter/OnlineVoterRegFormBlank.pdf
Your form must be mailed to:
Voter Registration
Lehigh County Government Center
17 S. 7th St.
Allentown, PA 18101-2401