William J. Alldridge (March 18, 1879 – June 9, 1942) was an American machinist from Milwaukee who served two terms as a Socialist member of the Wisconsin State Assembly representing the 5th Milwaukee County district (the 5th and 12th Wards of the City of Milwaukee).

[1] He later became a member of the Milwaukee Common Council, attended law school, and became a lawyer.

Alldridge had never run for or held public office until he was elected to the Assembly in 1904, receiving 1,629 votes against 1,568 votes for Republican William T. Duke, 1,518 for Democrat Joseph O'Hearn (Democratic incumbent Frank Hassa was not a candidate for re-election) and 34 for Charles M. Frink, an independent Democrat.

[2] He was re-elected in 1906, with 1503 votes against 1015 for Republican Frank Ammon and 887 for Democrat John Desseler.

[5] In later years he graduated from Marquette University Law School and became a lawyer.