Two Irvin/Erwin Zatrows are listed in the 1930 & 1940 censuses that were born abt 1901 in Wisconsin.  I'm farely confident this is the one whose spouse is Catherine (probably maiden name Kloosterman) and who lived in Illinois in 1940.  The other one (whose name was most frequently spelled as Ervin) was married to Mable Damerow and stayed in Wisconsin.
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6 MAY 1930 Oshkosh, Winnebago, Wisconsin
ED 34 Sheet 35B 203/233
Irvin Zastrow Male 29 Married White 1901 Wisconsin Wisconsin Illinois Head electrical engineer
Catharine Zastrow Female 27 Married White 1903 Wisconsin Wisconsin Minnesota Wife
18 apr 1940 Ward 3, Berwyn, Berwyn Township, Cook, Illinois
ED 16-15 Sheet 17A 433
Irvin Zastrow Sheboygan, Sheboygan, Wisconsin Male 39 Married White 1901 Wisconsin Head electrical engineer
Cathrine Zastrow Sheboygan, Sheboygan, Wisconsin Female 37 Married White 1903 Wisconsin Wife
Marge Zastrow Sheboygan, Sheboygan, Wisconsin Female 6 Single White 1934 Wisconsin Daughter